
==== Front
Eur J Sport Sci
Eur J Sport Sci
10.1002/(ISSN)1536-7290
EJSC
European Journal of Sport Science
1746-1391
1536-7290
John Wiley and Sons Inc. Hoboken

39167610
10.1002/ejsc.12182
EJSC12182
Original Paper
ORIGINAL PAPER
Sports and Exercise Medicine and Health
Criterion‐related validity and reliability of the standing long jump test in adults: The Adult‐Fit project
Marin‐Jimenez Nuria https://orcid.org/0000-0002-0687-7554
1 2
Perez‐Bey Alejandro https://orcid.org/0000-0002-9849-5544
1 2
Cruz‐Leon Carolina https://orcid.org/0000-0001-9070-5693
1 2 carolina.cruz@uca.es

Conde‐Caveda Julio https://orcid.org/0000-0002-2788-231X
1 2
Segura‐Jimenez Victor https://orcid.org/0000-0001-8655-9857
1 2 3 4
Castro‐Piñero Jose https://orcid.org/0000-0002-7353-0382
1 2
Cuenca‐Garcia Magdalena https://orcid.org/0000-0002-8510-9253
1 2
1 GALENO Research Group Department of Physical Education Faculty of Education Sciences University of Cadiz Puerto Real Spain
2 Instituto de Investigación e Innovación Biomédica de Cádiz (INiBICA) Cadiz Spain
3 UGC Neurotraumatología y Rehabilitación Hospital Universitario Virgen de las Nieves of Granada Granada Spain
4 Instituto de Investigación Biosanitaria ibs.GRANADA Granada Spain
* Correspondence
Carolina Cruz‐Leon, GALENO Research Group, Department of Physical Education, School of Education, University of Cádiz, Avenida República Saharaui s/n, Puerto Real (Cádiz) 11519, Spain.
Email: carolina.cruz@uca.es

21 8 2024
9 2024
24 9 10.1002/ejsc.v24.9 13791392
01 7 2024
07 2 2024
06 8 2024
© 2024 The Author(s). European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Abstract

The purpose of this study was to analyze the criterion‐related validity and the reliability of the standing long jump test (SLJ) for evaluating the lower‐body explosive muscular strength in adults. A total of 410 adults participated in this study. Sociodemographic, anthropometric measurements, laboratory lower‐body muscular strength tests, and the field‐based SLJ were performed. In validity analysis, stepwise regression analysis showed that maximal horizontal power, sex, percentage of body fat, maximal horizontal force, and lean mass were significantly associated with the SLJ distance (R 2 = 0.78; p < 0.001). Reliability analysis showed significant differences between test–retest in the SLJ test, with an overestimation of the second measurement compared to the first [12.14 ± 14.46 cm, intraclass correlation coefficient (ICC) = 0.94 (0.75–0.97), p < 0.001; Cohen's d = 0.31]. The coefficient of variation (CV) was 7.06% and the minimal detectable change (MDC90) was 29 cm. After a learning period, higher reliability values were found [0.45 ± 1.04 cm, ICC = 1.00 (0.99–1.00); p = 0.001; CV = 0.53 %; MDC90 = 1 cm]. The SLJ test may be a valid tool to assess lower‐body explosive muscular strength in the adult population. A learning period may be necessary to provide reliability on the SLJ test.

Highlights

The standing long jump (SLJ) test is the most used field‐based test for assessing lower‐body explosive muscular strength. However, its criterion‐related validity and reliability have not been explored in the adult population.

The SLJ is a valid test. Maximal horizontal power, sex, percentage of body fat, maximal horizontal force, and lean mass account for validity variance in SLJ distance.

The SLJ test is a reliable tool, regardless of sex, age and physical activity levels. It may be beneficial to implement a familiarization period before evaluation to ensure reliability.

The SLJ test is practical, time‐efficient, and low in cost and equipment requirements.

adults
criterion‐related validity
field test
lower‐body strength
reproducibility
Ministry of Education, Culture, and Sport 10.13039/501100003176 FPU19/02961 Ministry of Economy, Industry, and Competitiveness 10.13039/501100003329 DEP2017‐88043‐R PN / EPIF‐FPU‐CT / CP / 2021‐056 Regional Government of Andalusia and University of Cadiz: Research and Knowledge Transfer FundPPIT‐FPI19‐GJ4F‐10 source-schema-version-number2.0
cover-dateSeptember 2024
details-of-publishers-convertorConverter:WILEY_ML3GV2_TO_JATSPMC version:6.4.8 mode:remove_FC converted:03.09.2024
==== Body
pmc1 INTRODUCTION

Muscular strength has shown to have a protective effect on health, being positively associated with a reduction in all‐cause mortality by up to 31% (García‐Hermoso et al., 2018a, 2018b). The role of muscular strength has been recognized both in the prevention and treatment of chronic diseases, such as cancer (García‐Hermoso et al., 2018a, 2018b), multiple sclerosis (Sandroff et al., 2016), and diabetes (Tarp et al., 2019). Additionally, muscular strength is inversely associated with greater mental health, lower anxiety disorders, and depression (Jiang et al., 2022). Therefore, it would be interesting to assess muscular strength as a diagnostic criterion for evaluating health status.

In this regards, field‐based fitness tests are relatively safe and time‐efficient, involve minimal equipment and low cost, and can be easily administered to a large number of people simultaneously (España‐Romero et al., 2010), becoming a useful and reasonable tool for physical fitness assessment. Thus, the standing long (broad) jump (SLJ) test could be proposed as a lower‐body explosive muscular strength tool, since it is proposed in health‐related fitness test batteries to assess lower‐body explosive muscular strength in preschoolers (Ortega et al., 2015), children, and adolescents (Ruiz et al., 2011), given its known criterion‐related validity (the extent to which a field‐based test correlates with the criterion measure, that is, the gold standard) (Docherty, 1996) and reliability (indicating consistent results from a test performed multiple times under identical conditions in a short time span) (Hopkins, 2000). However, to our knowledge, the criterion‐related validity of this test has not been explored in adult population (Castro‐Piñero et al., 2021). Moreover, a recent systematic review has concluded that the SLJ test has moderate to high reliability, only in adults aged 18–45 years (Cuenca‐Garcia et al., 2022). In addition, the samples of the two included studies were young adults (Tsigilis et al., 2002) and military and civilian adults (Whitehead et al., 2012). Therefore, a broader overview is needed, including the full age range of the adult population (i.e., 18–64 years), with different PA levels, to analyze whether it could affect its reliability.

In view of the close relationship between lower‐body muscular strength and health in adults (García‐Hermoso et al., 2018a, 2018b; Ruiz et al., 2008), it would be advisable to determine the criterion‐related validity and reliability of the SLJ test in this population to use it as a health evaluation tool through field‐based fitness tests. Therefore, the aim of this study was to analyze the validity and the reliability of the SLJ test to assess the lower‐body explosive muscular strength in adults (i.e., 18–64 years), according to sex, age, and PA levels.

2 MATERIAL & METHODS

2.1 Study design

The present study is part of a national project: the ADULT‐FIT study (REF: DEP2017‐88043‐R), whose main aim was to propose a field‐based physical fitness test battery related to health based on their criterion–validity, predictive validity, reliability, feasibility, and safety for use in adults.

2.2 Participants

Sample size was calculated according to the sampling formula for infinite populations with a 5% significance level and a power of 95% and considering a dropout rate of 10% (Cochran, 1977). A total of 427 participants aged 18–64 years were recruited through leaflets, local newspapers, and social media from Cadiz (Spain). Finally, a total of 410 participants were included in this study homogeneously distributed by sex, age (18–34 years, 35–49 years, and 50–64 years), and PA level (non‐active and active).

The inclusion criteria for this study were (i) being an adult (18–64 years old), (ii) not having physical or mental illness that prevents you from doing PA, (iii) having intention to carry out all the tests included in the study, and (iv) being able to read and understand the informed consent as well as the object of the study. The exclusion criteria for this study were (i) having acute or terminal illness, (ii) myocardial infarction 3 months before starting the study, (iii) unstable cardiovascular disease, (iv) medical prescription that prevents the performance of the tests, and (v) injury or circumstance that makes it impossible to carry out the tests correctly.

All interested volunteers provided written informed consent to participate in the present study. The study was approved by the Committee for Research of Cadiz, Spain.

2.3 Testing procedures

After providing written informed consent and being informed of the protocol to be carried out, they signed the “Physical Activity Readiness Questionnaire” (PAR‐Q) (Adams, 1999) to detect possible contraindications to the practice of physical exercise and a questionnaire to determine the PA level of the participants.

Participants were randomly allocated according to sex, age, and PA levels, following the same protocol along the study process. This research was conducted in two phases. The first testing session (first phase) allowed for comparison between the laboratory and the field‐based test to analyze the criterion‐related validity of the SLJ (i.e., force platform and isokinetic vs. SLJ test), while the second testing session (second phase) allowed the comparison between sessions' performance in order to analyze the reliability of the SLJ test.

In the first appointment, sociodemographic, anthropometric measurements, and laboratory lower‐body explosive muscular strength assessment (including the SLJ test evaluated with a force platform and the isokinetic‐isometric testing) were carried out. Participants were instructed to rest 24 h before evaluations and to maintain their eating and hydration habits.

All participants completed a standardized 10‐min warm‐up, and then the SLJ test was performed first, given that this test implies the least strain on the musculature of the body than the other tests. After sufficient resting time (5–10 min depending on the self‐perceived fatigue of each participant), the isokinetic–isometric testing was performed. To become familiar with the isokinetic devices, 3 warm‐up repetitions were always performed in each isokinetic–isometric test. All participants received comprehensive instructions for each test and were encouraged to do their best at each attempt.

In the second appointment (1 week later), participants performed the SLJ test without the laboratory device (i.e., without force platform) in the same condition as before.

Since we found unexpected results for the SLJ test (i.e., participants performed systematically worse in the test compared with the retest), we decided to replicate the reliability study in a subgroup. Therefore, a randomly selected subgroup of 66 (33 females, median age 45 years) adults was additionally tested for the reliability of the SLJ test by including a learning period. This learning period comprised 3 sessions distributed on alternate days (Monday–Wednesday–Friday) for a week.

2.3.1 Physical activity levels

Participants were initially classified as active/non‐active when following/not following World Health Organization recommendations for adults (Organization, 2010). The following self‐reported question was asked: how many days (in a typical week) do you practice PA/exercise or some sport, of at least moderate intensity, lasting at least 50 min per day? Participants were classified as active if they adhered to these guidelines at least 3 days per week (i.e., accumulating at least 150 min of moderate intensity throughout the week).

2.3.2 Anthropometric assessment

Weight, height, waist and hip circumferences, and triceps and subscapular skinfolds were measured using the protocol described by the international society for the advancement of kinanthropometry (Marfell‐Jones et al., 2006). Measurements were performed by trained evaluators of the same sex as the participant.

All measurements were collected with baer feet, in light sports clothing, and with a 3‐h fast. The weight was measured using an OMRON BF‐400 electronic scale (Omron Healthcare Europe BV, Hoofddorp, The Netherlands; sensitivity, 100 gr). The established margin of error by which a third measurement should be made was a difference of 1 kg. The height was measured using a TANITA HR001 portable height rod (Tanita®, Illinois, USA; sensitivity, 1 mm). The margin of error that was established to make a third measurement was 1 cm. The body mass index (BMI) was calculated as weight (kg) divided by squared height (m2).

Waist and hip circumferences were assessed using the tape measure using SECA 201 (Seca Int, Hamburg, Germany; range, 0–205 cm; sensitivity, 0.1 cm). Tricipital and subscapular skinfolds were measured using the Harpenden Skinfold Caliper (Holtain, Dyfed, United Kingdom; range, 0–80 mm; sensitivity, 0.2 mm). The margin of error for a third measurement was 1 cm for circumferences and 1 mm for skinfolds.

The percentages of body fat (%BF) and lean mass (kg) were determined by using a multifrequency bioimpedance of 8 electrodes (TANITA‐MC780MA, Barcelona, Spain), according to the protocol described by the national institute of health (Research NIoHOoMAo, 1994) and the manufacturer's instructions. For its correct evaluation, the participants were asked about their level of hydration based on their urine color (Armstrong et al., 1998; Kostelnik et al., 2021).

2.3.3 Lower‐body muscular strength

The standing long jump tests

The SLJ is a simple test that assesses the participant's ability to generate explosive strength. The participants performed the SLJ test twice in two separate sessions. First time, the SLJ test was tested in laboratory conditions using the force platform (criterion‐related validity session, Figure S1A), and the second one was carried out in field‐based conditions (reliability session, Figure S1B). The same procedure was carried out in both sessions. In both conditions, the participant stood behind the starting line with their feet apart equal to the width of their shoulders and was instructed to push off vigorously and jump forward as far as possible. The participant had to land with the feet at the same time and to stay upright. The test was conducted twice, with the highest score, that is, the greatest distance achieved, being utilized for the analyses. A further attempt was allowed if the subjects fell backward or touched the floor with another part of the body (Castro‐Piñero et al., 2009). In the replication study, the same methodology as before was followed.

For laboratory assessment, a software “Measurement, Analysis and Reporting 5.0” (MARS) was used, connected to a Kistler force platform (Type 9428A, Kistler Group; Winterthur, Switzerland). Maximal force (%BF), maximal horizontal and vertical force (%BF), maximal power (W/kg), maximal horizontal and vertical power (W/kg), jump take‐off velocity (m/s), horizontal and vertical jump take‐off velocity (m/s), push off force impulse (Ns), and horizontal and vertical push off force impulse (Ns) were recorded during the SLJ test (Beckham et al., 2014). In both conditions (i.e., laboratory and field‐based test assessments), the distance was measured in cm, from the take‐off line to the point where the back of the heel nearest to the take‐off line landed on the floor.

Isokinetic testing

The isometric and isokinetic (60°/s) strength of the lower body was assessed using a HUMAC NORM isokinetic dynamometer (Cybex Isokinetic Dynamometer; Humac Norm), being calibrated according to the operation manual. The validity and reliability of this device for assessing lower‐body strength are high (Habets et al., 2018; Mellemkjær et al., 2024).

The dominant and non‐dominant legs were evaluated. Participants were seated with a hip flexion of 110° with the trunk upright and leaning against the back of the chair, secured with safety belts at the level of the shoulders, abdomen, and mid‐thigh of the evaluated leg (to reduce awkward movements during contractions) (Francis et al., 2017; Harbo et al., 2012). The participant was fitted with a proximal shin pad 4–5 cm from the medial malleolus on the tibia of the tested leg on which he/she exerted pressure (Francis et al., 2017). The axis of rotation of the dynamometer was aligned with the femoral condyle (axis of rotation of the knee joint).

At the beginning of the test, the participant's maximal relative knee extension 180° was calculated, considering this the absolute zero (point at which gravity acts vertically) (Francis et al., 2017) and the 90° flexion was calculated based on this measurement.

First, an isometric test of knee extension at 60° was developed in which the participant executed 3 maximal repetitions preceded by 3 warm‐up repetitions (Harbo et al., 2012). The maximal isometric peak torque was recorded (Nm). Secondly, a 60 deg/s test was performed in which 3 maximum concentric flexion‐extensions were executed preceded by a warm‐up of 5 progressive repetitions with the same gesture (Croisier et al., 2008). Maximal flexion and extension peak torque (Nm) per repetition (Nm) were recorded.

A 2‐min recovery period was always left between each test, and 1 min between warm‐up and test. Verbal motivation was given throughout the test and participants were told that the effort should be maximal (see Figure S2).

2.4 Statistical analyses

Means and standard deviations were calculated for all the variables. One‐way analysis of variance (ANOVA) was performed to assess significant differences between continuous variables and Chi‐square test for categorical variables.

Pearson's bivariate correlation was calculated to quantify the association between the SLJ test and anthropometric variables and laboratory lower‐body muscular tests. When significant, the strength of the correlations was classified as follows: 0.00–0.25, very low; 0.26–0.49, low; 0.50–0.69, moderate; 0.70–0.89, high; and 0.90–1.00, very high (Silva et al., 2015).

A stepwise linear regression model was conducted to examine the contribution of the different laboratory test variables to the explained variance of the SLJ distance. The SLJ distance was introduced as the dependent variable. Sex, age, PA levels, %BF, and lean mass were introduced in the model (enter method), in addition to the laboratory variables that presented a higher correlation. Variables were excluded from the model when p > 0.05.

Relative reliability of the field SLJ test was investigated through t‐test and intraclass correlation coefficient (ICC) and 95% confidence intervals. ICC ranges from 0 to 1, with values >0.9 being considered high reliability (Vincent‐Smith et al., 1999).

We also examined the differences between test and retest (hereafter called T1 and T2) using different error measures. Generally, the lower the error value, the lower the dispersion between T1 and T2 measurements. The sum of squared errors (SSE) was calculated as follows: SSE = ∑i=1Nyi−y^ 2, where n is the case to evaluate the error measurements, y^ is the T2, and y is the T1. The mean SSE (MSE): MSE = 1N∑i=1Nyi−y^ 2. The root mean SSE (RMSE) was calculated by converting MSE into domain units by taking the root square: RMSE = MSE. The percentage error was calculated as follows: %Error = RMSEymax−ymin × 100.

The following methods were used to study absolute reliability: standard error of measurement (SEM) as the percentage of the mean value of the measurements, standard error of estimate (SEE), the coefficient of variation (CV), and 95% limits of agreement (LoA) using the Bland–Altman plots (Bland et al., 1986, 1995), whose difference was calculated using an ANOVA test for repeated measures. These measures were calculated as follows: %SEM = mean of the difference scores between 2 trials × 100/mean of the first trial, with a value of SEM ≤ 15% considered as acceptable (Weir, 2005); SEE = SDy^(1−R2yy^); CV = δX‾ × 100, with a CV ≤ 10% considered as acceptable (Brown, 1998). In addition, the CV method provides useful information in the presence of heteroscedasticity (assumes that greatest T1 and T2 variation occurs in individuals scoring the highest values in the test). Finally, to estimate the smallest change in score that indicates a “real change” in 90% of participants, the minimal detectable change (MDC90) (Del Corral et al., 2020) was also calculated: MDC90 = SEM × 2 × 1.65. Heteroscedasticity was also identified by conducting regression analysis. A significant association (p < 0.05) between the difference and the magnitude of the measurement confirms heteroscedasticity (Atkinson et al., 1998).

Finally, Cohen's d was computed to quantify the magnitude of the difference between T1 and T2. Cohen's d values of 0.8, 0.5, and 0.2 represented large, medium, and small effect sizes, respectively (Cohen, 2013).

We conducted the analyses for the whole sample, as well as separately by sex, age groups, and PA levels, for all criterion‐related and reliability analyses.

All the analyses were performed using the statistical package for social sciences (IBM SPSS Statistics for Windows, version 26.0) and the level of significance was set at p < 0.05.

3 RESULTS

The descriptive characteristics of the participants, distributed by sex, age groups, and PA levels are shown in Table 1. The mean age of the sample was 42 (±13.06) years old. Overall, significant differences were found by sex, age groups, and PA levels.

TABLE 1 Descriptive characteristics of the participants, stratified by sex, age, and physical activity levels.

	All (n = 410)	Sex	Age groups	Physical activity levels	
Females (n = 203)	Males (n = 207)	18–34 years (n = 136)	35–49 years (n = 131)	50–64 years (n = 143)	Non‐active (n = 195)	Active (n = 215)	
Age (years)	41.86 (13.06)	41.48 (12.84)	42.24 (13.28)	26.22 (0.36)	42.49 (0.36)	56.17 (0.35)	43.18 (13.10)*	40.62 (12.95)	
Weight (kg)	71.16 (15.49)	62.06 (9.36)***	80.13 (15.12)	68.80 (16.24)	72.19 (16.29)	72.48 (13.77)	71.99 (16.82)	70.32 (14.14)	
Height (cm)	168.25 (9.19)	161.38 (5.98)***	175.00 (6.36)	168.46 (0.79)	168.42 (0.80)	167.89 (0.77)	167.33 (9.17)	169.02 (9.12)	
Body Mass index	24.99 (4.10)	23.85 (3.45)***	26.12 (4.38)	24.07 (4.27)a^	25.32 (4.48)	25.56 (3.38)c^^	25.55 (4.62)**	24.47 (3.50)	
Waist circumference (cm)	83.14 (12.66)	76.90 (9.25)***	89.26 (12.58)	78.11 (11.68)a^^	83.28 (13.11)b^^	87.80 (11.34)c^^^	85.54 (14.21)***	80.91 (10.64)	
Hip circumference (cm)	99.38 (8.69)	98.80 (7.27)	99.95 (9.87)	98.69 (9.75)	100.30 (9.19)	99.19 (6.96)	101.13 (9.10)***	97.77 (8.00)	
Tricipital skinfold (mm)	16.92 (7.48)	19.69 (6.42)***	14.23 (7.46)	16.13 (0.64)	17.03 (0.65)	17.58 (0.63)	19.39 (7.67)***	14.72 (6.56)	
Subscapular skinfold (mm)	19.50 (10.27)	20.33 (9.19)	18.68 (11.19)	17.37 (11.72)	19.46 (9.83)	21.57 (8.72)c^^	22.74 (10.99)***	16.57 (8.62)	
Body fat (%)	24.85 (7.47)	28.64 (6.30)***	21.11 (6.62)	22.77 (7.69)a^	24.99 (7.08)	26.70 (7.15)c^^^	27.38 (7.31)***	22.57 (6.89)	
Lean mass (kg)	50.37 (10.58)	41.56 (3.92)***	59.06 (7.41)	49.85 (10.13)	51.09 (10.81)	50.22 (10.83)	49.10 (10.72)*	51.45 (10.31)	
Standing long jump test, field‐based measurement	
Maximal long jump test (cm)	143.03 (38.53)	121.05 (28.86)***	164.37 (34.57)	159.64 (35.01)a^	146.26 (36.66)b^^^	121.41 (33.31)c^^^	131.48 (36.18)***	153.88 (37.52)	
Maximal long jump retest (cm)	155.68 (39.95)	133.00 (29.56)***	177.67 (36.30)	172.20 (37.30)	163.10 (37.75)b^^^	133.55 (34.10)c^^^	143.86 (37.10)***	166.73 (38.70)	
Standing long jump test, force platform measurement	
Maximal force (%BF)	194.97 (24.47)	192.39 (23.07)*	197.48 (25.58)	202.94 (25.49)a^^	194.12 (21.89)b^^^	188.16 (23.67)	189.62 (23.61)***	200.01 (24.26)	
Maximal horizontal force (%BF)	63.96 (16.90)	57.84 (14.60)***	69.92 (16.89)	73.79 (15.96)a^^^	65.60 (14.32)b^^^	53.10 (13.37)c^^^	59.37 (15.69)***	68.34 (16.77)	
Maximal vertical force (%BF)	186.49 (22.68)	185.96 (21.92)	187.02 (23.45)	192.16 (23.23)a^	185.01 (20.94)	182.46 (22.78)c^^^	182.70 (22.50)***	190.07 (22.36)	
Maximal power (W/kg)	21.23 (10.70)	19.12 (9.28)***	23.30 (11.57)	25.47 (12.24)a^^	21.57 (9.37)b^^^	16.90 (8.39)c^^^	18.31 (9.60)***	24.00 (10.94)	
Maximal horizontal power (W/kg)	12.36 (5.96)	10.02 (4.52)***	14.63 (6.31)	15.84 (6.09)a^^^	12.82 (5.32)b^^^	8.62 (3.89)c^^^	10.60 (5.05)***	14.02 (6.26)	
Maximal vertical power (W/kg)	16.73 (8.68)	15.61 (7.88)**	17.82 (9.28)	19.46 (10.01)a^	16.81 (7.65)b^	14.06 (7.33)c^^^	14.64 (7.87)***	18.70 (8.95)	
Jump take‐off velocity (m/s)	2.38 (0.61)	2.15 (0.50)***	2.61 (0.62)	2.68 (0.56)a^^	2.45 (0.55)b^^^	2.04 (0.53)c^^^	2.18 (0.54)***	2.57 (0.61)	
Horizontal jump take‐off velocity (m/s)	2.19 (0.57)	1.98 (0.48)***	2.40 (0.57)	2.47 (0.50)a^^	2.26 (0.52)b^^^	1.86 (0.51)c^^^	2.03 (0.53)***	2.35 (0.56)	
Vertical jump take‐off velocity (m/s)	0.73 (0.61)	0.62 (0.60)***	0.84 (0.61)	0.89 (0.59)	0.71 (0.63)	0.60 (0.59)c^^^	0.59 (0.55)***	0.86 (0.64)	
Push off force impulse (N_s)	79.18 (46.47)	61.51 (36.24)***	96.42 (48.91)	93.24 (48.95)	82.86 (43.16)b^^^	62.45 (41.88)c^^^	67.85 (44.18)***	89.92 (46.06)	
Horizontal push off force impulse (Ns)	155.43 (58.77)	122.64 (33.07)***	187.42 (60.76)	171.14 (55.25)	159.46 (66.60)b^^	136.80 (48.84)c^^^	144.97 (59.08)***	165.10 (57.08)	
Vertical push off force impulse (Ns)	51.90 (43.24)	37.31 (35.78)***	66.14 (45.18)	61.34 (41.78)	52.49 (44.13)	42.39 (12.03)c^^^	42.92 (39.76)	60.36 (44.74)	
Isokinetic	
Maximal isometric peak torque (N_m)	146.83 (51.82)	113.14 (31.16)***	179.86 (46.53)	162.89 (52.74)a^	147.64 (50.62)b^	130.80 (47.31)c^^^	136.05 (47.97)***	156.08 (52.91)	
Maximal 60/60 flexion peak torque (Nm)	73.73 (29.73)	60.07 (14.44)***	92.48 (26.10)	84.72 (28.36)	78.59 (25.65)b^^^	66.57 (22.53)c^^^	70.74 (23.41)***	81.34 (28.15)	
Maximal 60/60 extension peak torque (Nm)	103.57 (44.28)	82.36 (23.57)***	131.88 (38.23)	121.39 (40.24)a^	109.23 (39.83)b^^^	92.31 (40.31)c^^^	98.07 (35.43)***	115.79 (42.50)	
Maximal 60/60 flexion peak torque, per repetition (Nm)	84.68 (34.47)	69.40 (16.84)***	105.81 (31.09)	97.25 (32.86)	90.45 (29.53)b^^^	76.32 (26.71)c^^^	81.45 (27.05)***	93.21 (32.95)	
Maximal 60/60 extension peak torque, per repetition (Nm)	105.94 (46.32)	83.98 (24.89)***	135.16 (40.72)	123.88 (42.81)	112.03 (42.40)b^^^	94.42 (36.83)c^^^	100.95 (37.09)***	117.51 (45.12)	
Note: Results are expressed as mean (standard deviation). Difference between sex and physical activity levels measured with an independent t‐test, difference between age groups measured with the one‐way repeated measure analysis of variance (ANOVA).

Differences between sex and between physical activity levels: *p < 0.05, **p < 0.01, ***p < 0.001; differences between age groups: a = 18–34 years and 35–49 years, b = 35–49 years and 50–64 years, c = 18–35 years and 50–64 years (^ p < 0.05; ^^ p < 0.01, p ^^^<0.001).

3.1 Validity

Bivariate correlation analysis between the SLJ field‐based test and the laboratory lower‐body muscular tests and anthropometrics variables are displayed in Table 2. The SLJ distance was associated with all studied laboratory variables (all, p < 0.01). Maximal horizontal power (r = 0.826), maximal horizontal force (r = 0.815), jump take‐off velocity (r = 0.768), and horizontal jump take‐off velocity (r = 0.766) presented the highest associations with SLJ. All the isokinetic variables showed moderate associations (r = from 0.658 to 0.672; all, p < 0.01). The SLJ distance was associated with all anthropometric variables (all, p < 0.01), except for waist circumference (p > 0.05). %BF, sex, height, tricipital skinfold, and sum triceps + subscapular skinfold had moderate associations with the SLJ distance (r from −0.495 to −0.665; all, p < 0.01). Similar results were found when the sample was distributed by sex and PA levels. Regarding age groups, in the 50–64 years group, jump take‐off velocity and horizontal jump take‐off velocity presented moderate associations (r = 0.620 and 0.608, respectively; both p < 0.01) (Table S1).

TABLE 2 Bivariate correlation analysis between standing long jump field‐based test, force platform and isokinetic measurements, and anthropometric variables.

	SLJ	Sex	Age	PA levels	Weight	Height	BMI	Waist circ.	Hip circ.	Tricipital SKF	Subscapular SKF	SUM tricipital + subscapular SKF	Body fat (%)	Lean mass	
SLJ	1	0.560**	−0.421**	0.286**	0.176**	0.531**	−0.137**	−0.079	−0.208**	−0.518**	−0.427**	−0.495**	−0.665**	0.481**	
Max. force	0.396**	0.104*	−0.288**	0.212**	−0.090	0.112*	−0.197**	−0.198**	−0.205**	−0.302**	−0.304**	−0.322**	−0.344**	0.069	
Max. H force	0.815**	0.358**	−0.535**	−0.266**	0.018	0.317**	−0.182**	−0.191**	−0.215**	−0.445**	−0.386**	−0.437**	−0.582**	0.280**	
Max.V force	0.259**	0.023	−0.212**	0.163**	−0.119*	0.044	−0.191**	−0.193**	−0.191**	−0.235**	−0.255**	−0.262**	−0.258**	0.002	
Max. power	0.460**	0.196**	−0.355**	0.266**	−0.072	0.196**	−0.221**	−0.228**	−0.221**	−0.356**	−0.349**	−0.374**	−0.400**	0.117*	
Maximal H power	0.826**	0.387**	−0.531**	0.287**	0.069	0.376**	−0.151**	−0.144**	−0.171**	−0.435**	−0.376**	−0.426**	−0.567**	0.332**	
Maximal V power	0.317**	0.127*	−0.279**	0.234**	−0.095	0.131**	−0.211**	−0.216**	0.206**	−0.300**	−0.306**	−0.323**	−0.312**	0.053	
Jump take‐off velocity	0.768**	0.373**	−0.458**	0.324**	0.052	0.389**	−0.184**	−0.162**	−0.202**	−0.446**	−0.398**	−0.444**	−0.562**	0.321**	
H jump take‐off velocity	0.766**	0.37**	−0.458**	0.287**	0.102*	0.402**	−0.127*	−0.106*	−0.133**	−0.392**	−0.337**	−0.382**	−0.518**	0.349**	
V jump take‐off velocity	0.294**	0.183**	−0.218**	0.214**	−0.044	0.178**	−0.171**	−0.147**	−0.172**	−0.267**	−0.254**	−0.275**	−0.287**	0.096	
Push off force impulse	0.528**	0.376**	−0.293**	0.238**	0.212**	0.387**	0.021	0.029	−0.010	−0.253**	−0.168**	−0.216**	−0.330**	0.369**	
H push off force impulse	0.659**	0.552**	−0.260**	0.171**	0.485**	0.614**	0.234**	0.339**	0.198**	−0.142**	0.045	−0.036	−0.279**	0.644**	
V push off force impulse	0.356**	0.334**	−0.202**	0.202**	0.237**	0.335**	0.087	0.089	0.050	−0.188**	−0.115*	−0.155**	−0.220**	0.323**	
Maxi. isometric peak torque	0.658**	0.645**	0.293**	0.194**	0.466**	0.669**	0.169**	0.258**	0.095	−0.316**	−0.156**	−0.237**	−0.434**	0.679**	
Max. 60/60 flex. peak torque	0.671**	0.609**	−0.318**	0.200**	0.446**	0.648**	0.159**	0.233**	0.092	−0.332**	−0.169**	−0.253**	−0.434**	0.667**	
Max. 60/60 ext. peak torque	0.672**	0.615**	−0.328**	0.217**	0.488**	0.661**	0.199**	0.270**	0.141**	−0.279**	−0.122*	−0.200**	−0.396**	0.678**	
Max. 60/60 flex. peak torque, P/R	0.668**	0.588**	−0.306**	0.191**	0.427**	0.627**	0.147**	0.212**	0.078	−0.329**	−0.174**	−0.254**	−0.433**	0.647**	
Max. 60/60 ext. peak torque, P/R	0.661**	0.604**	−0.310**	0.196**	0.490**	0.653**	0.208**	0.276**	0.153**	−0.271**	−0.112*	−0.191**	−0.379**	0.673**	
Abbreviations: BMI, body max index; Circ., circumference; Ext., extension; Flex., flexion; H, horizontal; Max., maximal; P/R, per repetition; PA, physical activity; SKF, skinfolds; SLJ, standing long jump; V, vertical.

*p < 0.05, **p < 0.01.

Table 3 shows the results from the stepwise lineal regression analysis of the SLJ test. Maximal horizontal power accounted for 68% of the explained variance. When sex, %BF, maximal horizontal force, and lean mass were added to the model, the explained variance went up to 78%. Age, PA levels, and horizontal jump take‐off velocity were not included in the model as no significant associations were found.

TABLE 3 Stepwise regression models assessing the association of the force platform variables with the standing long jump distance.

Step	β	r	R 2	R 2 change	p value	
1	Maximal horizontal power	0.827	0.827	0.682	0.683	<0.001	
2	Maximal horizontal power	0.716	0.866	0.751	0.067	<0.001	
Sex	0.282	<0.001	
3	Maximal horizontal power	0.632	0.878	0.771	0.021	<0.001	
Sex	0.216	<0.001	
% Body fat	−0.191	<0.001	
4	Maximal horizontal power	0.401	0.882	0.778	0.006	<0.001	
Sex	0.225	<0.001	
% Body fat	−0.171	<0.001	
Maximal horizontal force	0.252	0.001	
5	Maximal horizontal power	0.368	0.885	0.782	0.005	<0.001	
Sex	0.107	0.032	
% Body fat	−0.203	<0.001	
Maximal horizontal force	0.269	0.001	
Lean mass	0.131	0.004	
Abbreviations: β, standardized regression coefficient; r, correlation coefficients; R 2, adjusted coefficients of determination. Statistically significant associations (p < 0.05) are highlighted in bold.

3.2 Reliability

The test–retest reliability of the SLJ test is shown in Table 4. The mean difference between the SLJ test–retest presented an overestimation of T2 compared to T1 (12.14 ± 14.46 cm, p < 0.001, Cohen's d = 0.309). The ICC showed a high reproducibility [ICC = 0.94 (0.75–0.97), p < 0.001], and the analyzed error measurements were RMSE = 18.94 cm; CV = 7.06%; SEE = 14.48 cm; and MDC90 = 28.85 cm. Table S2 shows the test–retest reliability of the SLJ test, distributed by sex, age groups, and PA levels. Overall, similar results to those of the whole sample were found.

TABLE 4 Test–retest reliability of standing long jump in the whole sample and in a subsample after a learning period.

	T1 a	T2 a	Intertrial difference (T2‐T1) a	p value	Cohen's d	ICC (95% CI) b	SSE	MSE	RMSE	% Error	% SEM	% CV	SEE	MDC90	
Whole sample (n = 410)	
Standing long jump (cm)	143.03 ± 38.53	155.68 ± 39.95	12.14 ± 14.46	<0.001	0.309	0.94 (0.75–0.97)	139972.00	358.90	18.94	9.47	8.46	7.06	14.48	28.85	
Subsample after a learning period (n = 66)	
Standing long jump (cm)	142.41 ± 35.12	142.86 ± 35.26	0.45 ± 1.04	0.001	0.013	1.00 (0.99–1.00)	0.00	1.27	1.13	0.80	1.04	0.53	1.03	1.07	
Abbreviations: %CV, percentage coefficient of variation; %Error, percentage error; %SEM, standard error of measurement; CI, confident interval; ICC, intraclass correlation coefficients; MDC90, minimal detectable change; MSE, mean sum of squared errors; RMSE, root mean sum of squared errors; SEE, standard error of estimate; SSE, sum of squared errors. Statistically significant associations (p < 0.05) are highlighted in bold.

a T1 refers to test (trial 1) and T2 to retest (trial 2). T2‐T1 refers to retest (trial 2) minus test (trial 1). Values are displayed as mean ± SD.

b ICC was significant at p < 0.00.

Figure 1 shows the Bland–Altman plots of the SLJ test. The results show a mean difference (i.e., a systematic error between the occasions) of 12.14 cm with LoA = −16.20 to 40.48 cm. No heteroscedasticity was observed (p = 0.087). When the sample was distributed by sex, age groups, and PA levels, similar results to those of the whole sample were found (Figure S3).

FIGURE 1 Bland–Altman plot of standing long jump test. The central line represents the mean differences between the second trial (T2) and the first trial (T1). The upper and lower dotted lines represent the upper and lower 95% limits of agreement (mean differences ± 1.96 SD of the differences), respectively.

Table 4 and Figure 2 show the test–retest reliability of the SLJ test after a learning period. Significant mean differences between T1 and T2 were found in the SLJ distance (0.45 ± 1.04 cm, p = 0.001, d = 0.013). The ICC reported a high reproducibility [ICC = 1.00 (0.99–1.00), p < 0.001], and the analyzed error measurements were RMSE = 1.13; CV = 0.53%; SEE = 1.03; and MDC90 = 1.07 cm. The systematic error was 0.45 cm (95% LoA = −1.58–2.49). No heteroscedasticity was observed (p = 0.361).

FIGURE 2 Bland–Altman plot of standing long jump test after a learning period. The central line represents the mean differences between the second trial (T2) and the first trial (T1). The upper and lower dotted lines represent the upper and lower 95% limits of agreement (mean differences ± 1.96 SD of the differences), respectively.

4 DISCUSSION

The aim of the present study was to analyze the criterion‐related validity and the reliability of the SLJ test to assess lower‐body explosive muscular strength in adult population, according to sex, age, and PA levels.

The main findings suggest that the SLJ test is valid and reliable to assess lower‐body explosive muscular strength in adults aged 18–64 years. Moreover, its validity is not determined by age or PA levels. Regarding reliability, it seems to depend on a prior familiarization period but not on sex, age, or PA levels.

The SLJ test is proposed to evaluate lower‐body explosive muscular strength related to health in children (Ortega et al., 2015) and adolescents (Ruiz et al., 2011), given its proven validity and reliability, while in adult population, there is a lack of evidence on its validity to date (Castro‐Piñero et al., 2021).

4.1 Validity

The SLJ test is a natural multi‐joint movement that involves taking off and landing with both feet in order to achieve maximum horizontal distance (Fernandez‐Santos et al., 2018). The performance of the SLJ test is partially influenced by variables such as the maximal force and velocity of the jump at the take‐off (Grosprêtre et al., 2018; Mackala et al., 2013) and anthropometric variables (height, weight, or %BF) (Podstawski et al., 2020). These findings are in line with our results. The SLJ distance was correlated with the force platform laboratory test and with the isokinetic laboratory test (r = 0.259–0.826; all, p < 0.001), especially with the platform variables, such as maximal horizontal power (r = 0.826), maximal horizontal force (r = 0.815), jump take‐off velocity (r = 0.768), and horizontal jump take‐off velocity (r = 0.766). Moreover, %BF, sex, height, tricipital skinfold, and sum triceps + subscapular skinfold had a moderate association with SLJ (r = −0.665–0.495; all, p < 0.001).

The fact that isokinetic variables were moderately associated with the SLJ test, in contrast with the stronger associations of the SLJ found with the force platform variables, may be partially explained by the different nature of the strength performance measured by both devices. The SLJ test was performed identically in two scenarios, laboratory, and field‐based performance, with the only particularity of the absence of the force platform in the SLJ field‐based test. Therefore, the strong correlations found between them may be explained by this fact. On the other hand, the isokinetic dynamometer evaluates lower‐body flexion and extension single‐joint movement, in a sitting position, isolating movements. In this sense, in a study conducted in collegiate football athletes, using a similar isokinetic 60/60 protocol that the one used in our study, found even weak correlations between the SLJ test and isokinetic variables (r = 0.28–0.36, all p < 0.05) (Smothermon, 2016). Thus, the validity of isokinetic devices seems limited in evaluating the performance in multi‐joint explosive exercises, such as SLJ. Alternatively, SLJ testing via a force platform may be more advisable.

In children and young population (6–17 years), the SLJ test is considered a general index of muscular fitness because of its strong association with other lower‐body explosive muscular strength tests (such as vertical jump, squat jump, and countermovement jump) (Castro‐Piñero et al., 2010; Fernandez‐Santos et al., 2015). Likewise, in children aged 7–12 years, Milliken et al. (2008) concluded that independently of BMI, the SLJ test would be considered a good predictor of lower‐body explosive muscular strength in children and young population (better even than the vertical jump test).

Maximal horizontal power, sex, %BF, maximal horizontal force, and lean mass accounted for 78% of the SLJ distance variance in the regression analysis. The SLJ follows a parabolic flight (Grosprêtre et al., 2018), and hence it appears reasonable that the variables related to the horizontal power path (Mackala et al., 2013) were the most predictable of the SLJ distance. In fact, in our regression model, the maximal horizontal power explained 68% of the variance in the SLJ distance. Additionally, maximal horizontal force increased the variance in the SLJ distance in 0.5%. In this sense, the fact that maximal horizontal power strongly influenced the SLJ distance may be explained by the fact that “power” is defined as force × velocity (Sale et al., 1991) or, in other words, as the ability of the lower limbs (mainly) to apply horizontal force with the highest speed. Therefore, the greater the ability to generate power at the take‐off, the longer the jump distance.

We observed that sex explained 7% of the variance in the SLJ distance. Physiologically, sex accounts for differences in power performance between females and males (Mayhew et al., 1990). Factors contributing to these differences are body composition, strength (due to muscle fiber type and muscle recruitment), and neuromuscular or glycolytic performance (Mayhew et al., 1990). Among body composition, lean mass is one of the main components influencing strength, and it seems that even controlling by lean mass, these differences still hold (Mayhew et al., 1990). Therefore, our results may confirm these sex differences, in terms of differences observe in physical fitness performance between females and males and as a predicting variable for SLJ distance. In addition, our results also confirm the partial influence of body composition showed in previous studies conducted in children (Fernandez‐Santos et al., 2015; Milliken et al., 2008), with %BF and lean mass together accounting for 2.6% of the explained variance in the SLJ distance.

On the other hand, age and PA levels showed no significant associations with SLJ distance. In children, central nervous system maturation may play a role in muscular strength performance, affecting the SLJ test (Fernandez‐Santos et al., 2018), whereby age or PA may be involved. In adults, this maturational status on SLJ performance seems not relevant, probably because noticeable changes in cognitive performance take time to manifest as changes in physical fitness performance (i.e., slower movements or reduced strength due to the natural aging process). As a consequence, it is possible that this lack of associations could be attributed to other factors, such as the jumping technique (Grosprêtre et al., 2018; Mackala et al., 2013), since most of our participants have no previous experience in performing this test. In fact, jumping skills in expert jumpers may increase SLJ performance (Grosprêtre et al., 2018).

Therefore, for all the aforementioned, we suggest that the SLJ is a valid test to be included as a fitness health tool in the adult population. In addition, lower‐body muscular strength has a close relationship with health and mortality in adults (García‐Hermoso et al., 2018a, 2018b). Whilst further investigations into the criterion‐related validity of this test are warranted, the SLJ assessment demonstrates potential.

4.2 Reliability

The mean difference between the SLJ test T1 and T2 presented an overestimation of 12.1 cm (p < 0.001), with a medium magnitude between these differences (d = 0.31). Moreover, the Bland–Altman plot showed a systematic error between trials and large LoA, although acceptable (Brown, 1998) %CV was found (CV = 7%), which suggests that the variability or relative dispersion between trials was low in the entire sample (Atkinson et al., 1998). However, the MDC90 was 29 cm, indicating that the real difference that can be expected between trials in the same individual is considerable (Haley et al., 2006). This may be due to an existing learning effect (systematic error) among these tests when repeated measurements are performed. These results remained the same regardless of sex, age groups, or PA levels.

To date, a recent systematic review (Cuenca‐Garcia et al., 2022) concluded, with moderate evidence (derived from two studies) (Tsigilis et al., 2002; Whitehead et al., 2012), that the SLJ test has moderate–high reliability (ICC = 0.89–0.98), with a low dispersion of T1 and T2 measurement errors (SEMs <15%; CV = 3%) in adults aged 18–45 years. Our results concur with it in terms of ICCs, showing even a lower SEM [ICC = 0.94 (0.75–0.97); SEM = 8%], also including adults aged >45 years. In addition, our study shows a more holistic view in regard to the reliability of the SLJ taking into account diverse reasons: a higher sample size (410 participants in our study vs. 179 and 95 participants in the others), a well‐balanced sex and PA sample distribution, and a full adult age range. All these characteristics (i.e., sex, age, and PA levels) were analyzed to evaluate the possible influence on reliability terms. In view of this, the SLJ test showed high reliability in adults aged 18–64 years old, independently of sex, age, and PA levels.

In young population (6–18 years) (España‐Romero et al., 2010), we have also observed a significant T1 and T2 difference in the SLJ distance (4 cm, p < 0.005), suggesting learning effects on the test. Nevertheless, another study (Fernandez‐Santos et al., 2015) found a high reproducibility [ICC = 0.94 (0.93–0.95)], without significant T1 and T2 differences in the SLJ, in children (6–12 years). However, in preschoolers (Cadenas‐Sanchez et al., 2016), significant differences were found in a first analysis attempt (−7.31 cm, p < 0.001), improving its reliability after some methodological adaptations (−2 cm, p < 0.001).

To confirm or contrast whether a learning effect might exist, we decided to replicate the SLJ test protocol in a subsample of 66 adults, including a learning period of 3 sessions. Since the systematic error and error measurements were substantially reduced (i.e., 12 vs. 0.45 cm; LoA −16.20–40.48 vs. −1.58–2.49; %CV 7 vs. 0.5; and MDC90 29 vs. 1 cm, T1 and T2, respectively), it can be confirmed that the SLJ test needs a familiarization period to be reliable.

Given that the SLJ technique can significantly influence performance aspects such as coordination between arms and legs, arm swings, and balance (Grosprêtre et al., 2018; Mackala et al., 2013), it is recommended that future studies include a familiarization period with more than three sessions. This would allow for the observation of potential similarities in reliability results. The learning effect observed between the initial test and retest across all groups can be attributed to the “practice effect”, a common phenomenon in research where participants undergo the same or similar tests multiple times (Baumgartner, 1969). In the context of the SLJ, this practice effect could be a result of participants gaining familiarity with the jump technique, developing a clearer understanding of the expectations or formulating strategies to enhance their performance.

To sum up, the SLJ test shows high reliability in adults aged 18–64 years, independently of sex, age, and PA levels. Although the SLJ is a simple field‐based test to evaluate lower‐body explosive muscular strength, a familiarization period is necessary to minimize any bias due to learning effects.

4.3 Limitations and strengths

The present study has limitations that must be underlined. Firstly, the first SLJ trial (i.e., T1) was performed on a force platform (laboratory test), while the second SLJ trial (i.e., T2) was performed on a resin sports flooring (field test), which could cause changes in the sport shoes grip during take‐off or landing, affecting the total distance of the test. However, anti‐slip tapes were placed in the landing area to ensure a safe and slip‐free landing.

Some strengths also need to be highlighted. First, the relatively large sample as well as the homogeny distribution of the sample by sex, age, and PA levels. Second, the analysis of several anthropometric variables, including height, weight, %BF, lean mass, triceps and subscapular skinfolds, and hip and waist circumferences, also constitutes a strength, to detect which may result in a more explanatory variable for the validity equations. Third, a wide number of laboratory variables were analyzed, using both an isokinetic device and a force platform. Fourth, a replication study in a subsample to demonstrate a familiarization period is mandatory to provide reliability in the SLJ test. Finally, although ICC, Bland–Altman, SEM, CV, and MDC90 are the most common statistics used to report reliability in sport medicine (Atkinson et al., 1998), we have also included different measurement errors to a more complete interpretation of reliability.

5 CONCLUSIONS

The SLJ test is a valid tool to assess the lower‐body explosive muscular strength in the adult population, independently of age, and PA levels. In particular, it was found to have a stronger association when testing male adults. Moreover, the SLJ test is also reliable regardless sex, age, and PA levels, although it seems advantageous to implement a familiarization period prior to evaluation to ensure reliability. Since the SLJ test is practical, time efficient, and low in cost and equipment requirements, we suggest the use of this test as a reliable and valid measurement of the lower‐body explosive muscular strength in adults when laboratory methods are not feasible.

CONFLICT OF INTEREST STATEMENT

The authors declare no competing interest.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

DECLARATION OF GENERATIVE AI IN SCIENTIFIC WRITING

Neither artificial intelligence was used in the writing of this manuscript nor in the data processing.

Supporting information

Supporting Information S1

ACKNOWLEDGMENTS

The authors thank our subjects for the time and effort they volunteered to complete this study. This project was supported by the Ministry of Economy, Industry, and Competitiveness in the 2017 call for R&D Projects of the State Program for Research, Development, and Innovation Targeting the Challenges of the Company; National Plan for Scientific and Technical Research and Innovation 2013–2016 (DEP2017‐88043‐R); National Plan for Scientific and Technical Research and Innovation 2017–2020 (PN/EPIF‐FPU‐CT/CP/2021‐056); the Spanish Ministry of Education, Culture, and Sport (FPU19/02961), and the Regional Government of Andalusia and University of Cadiz: Research and Knowledge Transfer Fund (PPIT‐FPI19‐GJ4F‐10).

DATA AVAILABILITY STATEMENT

Data availability under request.
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