
==== Front
J Phys Ther Sci
J Phys Ther Sci
JPTS
Journal of Physical Therapy Science
0915-5287
2187-5626
The Society of Physical Therapy Science

2024-049
10.1589/jpts.36.542
Original Article
Associations between whole-body reaction time, maximum jump height, and skeletal muscle mass when reaction time and jump height are investigated as a complex
Watanabe Manabu RPT, PhD 1 *
Watarai Koji MD 2
Katoh Munenori RPT, PhD 3
1) Faculty of Medical Science, Nippon Sport Science University: 122-1 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa 227-0033, Japan
2) Center for Medical Education, Teikyo University of Science, Japan
3) Department of Physical Therapy, Faculty of Health Science, SBC Tokyo Medical University, Japan
* Corresponding author. Manabu Watanabe (E-mail: watanabe-ma@nittai.ac.jp)
5 9 2024
9 2024
36 9 542545
26 4 2024
12 6 2024
2024©by the Society of Physical Therapy Science. Published by IPEC Inc.
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (by-nc-nd) License. (CC-BY-NC-ND 4.0: https://creativecommons.org/licenses/by-nc-nd/4.0/)
[Purpose] This study aimed to investigate the association between whole-body reaction time and maximum jump height as elements of agility performance requiring maximum jumping when measured separately as closed-skill sports or as a complex of open-skill sports and their association with skeletal muscle mass. [Participants and Methods] This study included 54 healthy adult volunteers. Reaction time and jump height in response to a light stimulus were measured separately (the “simple condition”) and simultaneously (the “complex condition”), and the associations between the values under these two conditions were investigated. The associations between the skeletal muscle mass and the two elements under both conditions were also investigated. [Results] No correlation was found between the reaction times measured under the simple and complex conditions; however, a significant correlation was evident for the jump height. Skeletal muscle mass correlated significantly with jump height but not with reaction time. [Conclusion] The study results suggest that the relationship between open- and closed-skill sports differs between reaction time and jump height. Therefore, closed-skill sports training may be insufficient for improving open-skill sports and cognitive function and may affect decision-making strategies.

Whole body reaction time
Jump
Open skill sports
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pmcINTRODUCTION

In jumping-based open skill sports (OSS), rapid, high jumps in response to an opponent’s reaction are important for agility performance. Young et al.1) and Sheppard et al.2) reported that cognitive factors are associated with agility movement speed, defined as “a rapid whole-body movement with change of velocity or direction in response to a stimulus”2). Measurement in response to the same stimuli as those occurring during OSS is therefore required2, 3). However, conventional agility tests, such as the stepping test and t-test, do not provide measurements that reflect OSS. Physical functions affecting one’s agility are their skill, the strength of leg muscles, cognitive functions, and decision-making strategy1). Accordingly, during games, athletes must react immediately to situations that change by the second4). In recent years, agility measurements that accurately represent the characteristics of sports performance have come into widespread use1, 3, 4).

Some studies of jump abilities in the context of agility have addressed parameters such as the Rebound Jump Index5). However, most have investigated jump height6). OSS require jumping quickly and high in response to an opponent’s movements. Ebben and Petushek7) used the Reactive Strength Index Modified (RSI mod) to measure plyometric performance. However, the RSI mod evaluates the time to maximum jump height in a vertical jump from a starting time determined by the participants. It is thus different from jump performance as a rapid reaction to an opponent’s movement. No study has previously investigated jump performance under the complex condition of the simultaneous measurement of whole-body reaction time and maximum jump height. This study investigated maximum jump height in a vertical jump (JH) and whole-body reaction time (RT). RT and JH were evaluated together as the “complex” condition, and RT or JH separately as the “simple” condition.

We hypothesized that “the correlation in JH between OSS and closed-skill sports (CSS) and the correlation in RT between OSS and CSS differ in degree”. In this study, we measured the three parameters of RT and JH under a complex condition reflecting OSS and a simple condition reflecting CSS and skeletal muscle mass (SMM). We investigated the correlations between RT and JH under complex and simple conditions. We also investigated the correlation of SMM with RT and JH under both conditions.

PARTICIPANTS AND METHODS

The study participants were 54 healthy adult volunteers (27 men and 27 women). Their body compositions are shown in Table 1Table 1. Body composition of participants

N	Age (years)	Height (cm)	Weight (kg)	Skeletal muscle mass (kg)	
54	20.6 (0.6)	165.8 (7.6)	63.0 (8.8)	26.7 (5.6)	
Mean (standard deviation).

. Body composition measurements were made by measuring weight and SMM at baseline with a body composition analyzer (InBody470, Seoul, South Korea).

This study was approved by the Nippon Sport Science University Institutional Review Board (no. 022-H060), and written informed consent was obtained from all the participants.

During the exercise task in this study, we measured JH and RT under simple and complex conditions. The measurements were made with a jump height/reaction time measurement device (Takei Scientific Company, Niigata, Japan) capable of measuring RT and JH simultaneously. JH measurements were conducted according to the method described in the Japan Institute of Sports Sciences FITNESS CHECK HANDBOOK8). Under the simple condition, we measured the RT of the most rapid jump in reaction to a light stimulus and the highest JH unrelated to a light stimulus. Under the complex condition, we simultaneously measured the RT and JH of a rapid jump as high as possible in reaction to a light stimulus.

The measurement procedure was as follows. (1) The participants stood up straight on a mat switch (50 cm × 60 cm) with their feet apart at the same width as their shoulders. (2) When a starting signal was sounded, they adopted a squatting position (SP) (Fig. 1aFig. 1. Jump height/reaction time measurement device and squatting position.

(a) Squatting position: Both hands grasped the bilateral iliac crests, and the legs were positioned so they could jump immediately. (b) Measurement device: A jump height/reaction time measurement device (Takei Scientific Company) was used. Light stimulation device: The light blinked randomly after a starting sound was played.

). (3) When a light was flashed randomly (after between 1 and 3 s) by a light stimulation device, they jumped in accordance with the relevant exercise task (Fig. 1b). A standardized SP was adopted during all the exercise tasks, with both hands holding the bilateral iliac crests to prevent the arms from rebounding. The participants were instructed to maintain the SP at a subduction depth from which they could jump immediately (the angle of each leg joint was up to them) (Fig. 1a). Before the measurements were taken, the participants practiced the same jumping movements for the exercise tasks. Measurements were conducted three times for each exercise task, with a sufficient break between each task to prevent the participants from becoming tired.

We investigated the associations between RT and JH under the simple and complex conditions and their associations with SMM. The maximum and minimum values were excluded from the analysis, and the intermediate value was used. Spearman’s rank correlation coefficient was used for the statistical analysis of associations, with p<0.05 regarded as statistically significant.

RESULTS

Table 2Table 2. Whole body reaction time and maximum jump height under the simple and complex conditions

		n	Mean	SD	
Simple	RT	54	0.36	0.03	
JH	54	39.5	9.2	
Complex	RT	54	0.51	0.07	
JH	54	32.9	8.5	
Simple: Simple condition; Complex: complex condition; RT: Whole body reaction time (sec); JH: Maximum jump height (cm) in a vertical jump; SD: standard deviation.

shows the results of RT and JH measurements under the simple and complex conditions.

There was no correlation between RT under the simple and complex conditions (p=0.12, rs=0.24), but a positive correlation was evident for JH (p=0.001, rs=0.86).

There was no correlation between SMM and RT under the simple or the complex conditions (simple: p=0.22, rs=0.17; complex: p=0.54, rs=0.08). A positive correlation was evident between SMM and JH under the simple and complex conditions (simple: p=0.001, rs=0.69; complex: p=0.004, rs=0.51).

DISCUSSION

Our results showed that the RT under the simple condition was not affected by performing a rapid, high jumping movement under the complex condition. Because the RT under the simple condition was measured as a rapid reaction to a light stimulus in a simple task, cognitive elements related to the reaction played a greater role than elements related to leg muscle strength. Tsubouchi et al.3) also found that even when the RT was excellent for a single reaction, it declined with repeated tasks. The results of RT measurements in this study also showed that the RT under the simple condition did not affect its value under the complex condition. This suggested that different physical factors may be involved in agility in CSS and OSS. Under the complex condition, cognitive and decision-making elements are also required in addition to jumping skills and leg muscle strength.

There was a strong positive correlation between the values of JH under the simple and complex conditions. This suggested that jumping high depends on jumping skill and leg muscle strength rather than cognitive and decision-making elements.

SMM was not associated with RT under either the simple or the complex condition. However, it was strongly positively correlated with JH under the simple and complex conditions. Studies on jumping and body composition have shown that the body fat percentage negatively correlates with JH9, 10). The positive association between SMM and JH in this study reflects the result reported by Abidin et al10).

Like cognitive and decision-making elements, skills also contribute to agility1). The jumping movements in this study started from a squatting position that excluded subduction and arm rebound. Accordingly, a rapid high jump is impossible when the SP is not the optimum form. A suboptimal form is likely to result in either the induction of compensation or a lower jump. Depth of subduction and overall skill until takeoff are also important in the RSI mod7). Uchida et al.11) also considered that maintaining a readiness posture in anticipation of stimulus recognition, reaction, and movement is important. Motor movement skills are also important for rapid, high jumping movements under the complex condition. However, we did not use motion analysis for skills measurement in this study. The confirmation that this study can provide is thus limited.

In this study, we investigated RT and JH under the simple and complex conditions and their association with SMM. We showed that agility is different under the simple and complex conditions. Our results suggested that agility in OSS and CSS may include different physical elements. However, as we did not use motion analysis to investigate skills in this study and did not compare OSS athletes such as basketball and CSS athletes such as swimming, further studies are required.

Funding

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP22K17678.

Conflict of interest

None.
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