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Journal of Exercise Physiologyonline

August 2016 Volume 19 Number 4

Editor-in-Chief Tommy Boone, PhD, MBA Review Board Todd Astorino, PhD Julien Baker, PhD Steve Brock, PhD Lance Dalleck, PhD Eric Goulet, PhD Robert Gotshall, PhD Alexander Hutchison, PhD M. Knight-Maloney, PhD Len Kravitz, PhD James Laskin, PhD Yit Aun Lim, PhD Lonnie Lowery, PhD Derek Marks, PhD Cristine Mermier, PhD Robert Robergs, PhD Chantal Vella, PhD Dale Wagner, PhD Frank Wyatt, PhD Ben Zhou, PhD Official Research Journal of the American Society of

Exercise Physiologists

ISSN 1097-9751

Official Research Journal of the American Society of Exercise Physiologists

ISSN 1097-9751

JEPonline

Comparison of Factors Related to Jump Performance in Volleyball Players and Swimmers Mami Yoshimura, Yoshihisa Umemura Laboratory for Exercise Physiology and Biomechanics, Graduate School of Health and Sport Sciences, Chukyo University, Aichi, Japan

ABSTRACT

Yoshimura M, Umemura Y. Comparison of Factors Related to Jump Performance in Volleyball Players and Swimmers. JEPonline 2016;19(4):53-65. The purpose of this study was to compare the morphometry of Achilles tendon (AT), the stiffness of ankle joint, and the leg strength of swimmers with that of volleyball players. Further, the role of long-term training in the different playing styles was examined, as well as factors related to jump performance between the two groups. The subjects were 17 male swimmers (age, 20 ± 1 yrs; sport history, 15 ± 1 yrs; height, 174.6 ± 6.2 cm; body mass, 70.0 ± 6.9 kg) and 16 male volleyball players (age, 20 ± 1 yrs; sport history, 10 ± 2 yrs; height, 180.9 ± 4.0 cm; body mass, 76.3 ± 9.1 kg). The findings indicate that the volleyball group had a significantly greater AT length ratio and AT thickness than the swimming group. There were no significant differences between the swimming group and volleyball group in leg extension strength or stiffness of the ankle joint, although the swimming group had significantly greater range of motion than the volleyball group. The length of the AT and leg extension strength were factors that related to jump performance in the swimming group; however, this was not the case in the volleyball group. These results suggest that the morphology of the AT and the factors correlated to jump performance may change in accordance with the different exercise training over an extended period. Key Words: Jump Performance, Achilles Tendon Stiffness, Different Playing Characteristics, Different Adaptation

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INTRODUCTION In certain sports, jump ability is an important factor in determining performance. According to previous studies (3,9,11,15), physical characteristics, mechanical properties of the tendon and muscle, and leg muscle strength and power contribute to jump ability. However, in these studies, the authors have not always fully considered the career or exercise training mode of the subjects, making it difficult to determine whether the factors related to jump performance resulted from adaptations to jump training. Specifically, it is possible that different factors contribute to jump performance among subjects who carry out different exercise training over long periods. Volleyball players frequently perform jump movements characterized by large instantaneous power during actions such as spiking, serving, and blocking. In contrast, swimmers perform most characteristic movements in the water (except the dive movement), where loads are lightened by the buoyancy condition. The way that physical fitness and morphological characteristics adapt in relation to jump performance for athletes with extended exercise training of such different playing types is not well understood. Previous studies in which jumping-related factors were investigated did not investigate swimmers. Therefore, it is important to investigate the factors that determine the jump ability of swimmers compared with that of volleyball players. In this study, we investigated the morphometry of the Achilles tendon (AT), the stiffness of the ankle joint, and leg strength as factors associated with jump ability. With regard to Achilles tendon length (ATL) ratio, no significant differences among long-distance runners, volleyball players, and kayakers have been reported. To our knowledge, no studies have shown different ATL ratios between different types of athletes. However, the cross-sectional area (CSA) of the AT is greater in runners compared with non-runners and greater in volleyball players compared with kayakers. In addition, it was reported that short-term plyometric training significantly enlarged the CSA but not the length of the AT. These studies suggested that large intermittent loads enlarge the CSA of the AT. However, how the AT adapts to swimming training compared with training with gravity is not clear, nor is the adaptation of ankle joint stiffness and leg strength to swimming training. Therefore, in this study, we compared the morphometry of AT, the stiffness of the ankle joint, and the leg strength of swimmers with that of volleyball players. Further, we examined how each measured variable adapted during long-term training with the different playing styles, as well as how the factors involved in jump performance differed between the two groups. METHODS Subjects The subjects were 17 male swimmers (age, 20 ± 1 yrs; sport history, 15 ± 1 yrs; height, 174.6 ± 6.2 cm; body mass, 70.0 ± 6.9 kg) and 16 male volleyball players (age, 20 ± 1 yrs; sport history, 10 ± 2 yrs; height, 180.9 ± 4.0 cm; body mass, 76.3 ± 9.1 kg). All subjects belonged to the university’s sports teams and did not have any injuries to their lower limbs. Moreover, the volleyball players who were recruited played the “attacker” position and jumped well during routine practice. Each subject was informed of the purpose, procedure, and possible

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risks of the study in oral and written form. This study was carried out after obtaining informed consent in writing from all subjects. Informed consent was obtained from the parents of minor subjects. This study was approved by the Research Ethics Committee of Chukyo University. Procedures Height, Body Mass, and Morphometry of the AT The measured morphological characteristics were height, body mass, the center of the popliteal fossa (CPF), ATL, and AT thickness (ATT). ATL was defined as the length from the gastrocnemius muscle tendon junction to the AT calcaneus stop portion for the right leg and was measured using an ultrasound system (LOGIQ P5; GE Healthcare, Little Chalfont, UK) (Figure 1). CPF was defined as the length from the floor to the wrinkle at the center of the popliteal fossa for the right leg. In addition, the ratios of ATL to CPF (ATL/CPF), ATL to height (ATL/H), and CPF to height (CPF/H) were calculated. ATT was measured using an ultrasound system in the horizontal plane at the height of the lateral malleolus of the right foot (Figure 2). (a) (b)

Figure 1. The Achilles Tendon Length (ATL) was Measured with the Subject in the Prone Position on the Bed. ATL was defined as the length from the gastrocnemius muscle tendon junction to the AT calcaneus stop portion and measured using an ultrasound system for the right leg. “a” shows the muscle-tendon transition of the gastrocnemius. “b” shows the calcaneus stop part of the AT.

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Figure 2. Achilles Tendon Thickness (ATT) was Measured in the Same Position as the ATL (shown in Figure 1) and was Measured Using an Ultrasound System in the Horizontal Plane at the Height of the Lateral Malleolus of the Right Foot. ATT is the length between the arrows on the left in the figure.

Mechanical Properties of the Ankle Joint To evaluate the mechanical properties of the ankle joint, the ankle dorsiflexion angle and ankle joint passive torque were measured sequentially, and the muscle-tendon complex stiffness was calculated from these parameters. Subjects sat in the right knee maximum extended position in a isokinetic strength meter (System 3; Biodex Medical Systems, Inc., Shirley, NY, USA). The right foot was firmly secured with a belt to the foot plate. Then, the rotation axis of the foot plate and the position of the lateral malleolus were set in a straight line (Figure 3).

Figure 3. For Evaluation of the Mechanical Properties of the Ankle Joint, Ankle Dorsiflexion Angle and Ankle Joint Passive Torque were measured sequentially, and the Muscle-Tendon Complex Stiffness was calculated from these values. While the foot plate was rotated at a speed of 1°·sec-1, the dorsiflexion angle and ankle joint passive torque were measured throughout the ankle range of motion (ROM).

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In this study, we defined ankle joint angle at 0° (dorsiflexion 0°) when the foot plate was perpendicular to the ground and measured the ankle joint angle as the rotation angle of the foot plate; we defined dorsiflexion as positive. While the foot plate was rotated at a speed of 1°·sec-1, the dorsiflexion angle and ankle joint passive torque were recorded throughout the ankle’s range of motion (ROM). The angle and torque were measured by the isokinetic strength machine. These data were converted from analog to digital date at a sampling rate of 1.5 kHz using a data recorder (LX-10; TEAC Corporation, Tokyo, Japan). In determining ROM, the subjects were instructed to press the stop button if they felt pain. During this process, the subjects were blindfolded to remove possible visual bias. Three ROM trials were carried out for each subject, and the trial with the highest ROM was used for analysis. Muscle-tendon complex stiffness was calculated from the slope of the ankle joint angle-passive torque curve, which was fitted by quadratic regression from the last 12° of ROM data (i.e., the maximal dorsiflexion ankle angle [MDA]). The stiffness was calculated at the MDA, MDA −4°, MDA −8°, and MDA −12°, in a similar manner as prior studies (4,14). Measurement of Jump Height The squat jump (SJ), counter movement jump (CMJ), and rebound jump (RJ) were measured as jump performance data. Each jump height was measured using a jump mat (Multi Jump Tester II; DKH Inc., Tokyo, Japan). In the SJ, the subjects jumped vertically from a static squat position. In the CMJ, the subjects jumped vertically after dropping from a standing position into a squat position. In the RJ, the subjects jumped eight times consecutively. During each jump, the subjects were instructed to jump without an arm swing to prevent their contribution to jump height. SJ and CMJ were measured several times; RJ was measured twice. The maximum values of the SJ and CMJ trials were recorded, while the trial with the higher average value of all eight jumps was recorded for the RJ. The subjects were allowed to rest as much as needed before the next trial. Leg Strength Subjects sat on the chair of the isokinetic strength meter, and their chest, abdomen, and thighs were fixed with the belt. Then, the subjects performed knee joint extension and flexion at maximum effort at a rotation speed of 60°·sec-1. Three trials were performed for each leg, and the maximum value was recorded. To become familiar with this measurement technique, the subjects first practiced at submaximal effort. Statistical Analyses The age of the subjects, their sports history, height, body mass, and other measured variables are shown as mean ± standard deviation. An unpaired t-test was used to test for significant difference between the two groups (volleyball vs. swimming). The correlations between measured variables and jump height were tested between the swimming and volleyball groups using Pearson’s product-moment correlation coefficient. Moreover, the correlations between AT parameters and jump height among all subjects were tested using Pearson’s product-moment correlation coefficient. The levels of significance were P<0.05 and P<0.01.

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RESULTS

Height, Body Mass, and Morphometry of AT A comparison of the physical characteristics of the swimming and volleyball groups is shown in Figure 4. The volleyball group had significantly greater height and body mass than the swimming group.

＊＊

＊＊

＊＊

＊＊

＊

＊＊

A B

C D

E F

G H

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Figure 4. Mean ± Standard Division of the Height (A), Body Mass (B), CPF (C), CPF/H (D), ATL (E), ATL/H (F), ATL/CPF (G), and ATT (H) in the Swimming Group (open bar) and the Volleyball Group (filled bar). Statistically significant differences between the swimming and volleyball groups are denoted as *P<0.05 and ** P<0.01; CPF = the center of the popliteal fossa, CPF/H = ratio of the center of the popliteal fossa per height, ATL = Achilles tendon length, ATL/H = ratio of Achilles tendon length per height, ATL/CPF = ratio of Achilles tendon length per the center of the popliteal fossa, ATT = Achilles tendon thickness.

The volleyball group had a significantly greater CPF than the swimming group. However, there were no significant differences in CPF/H ratio between the groups. The volleyball group also had significantly greater ATL, ATL/H ratio, and ATL/CPF ratio than the swimming group. In addition, the volleyball group had significantly greater ATT than the swimming group. ROM and Mechanical Properties of the Ankle Joint ROM was significantly greater in the swimming group than the volleyball group (Table 1). Muscle tendon complex stiffness at the ROM dorsiflexion endpoint (MDA), MDA −4°, MDA −8°, and MDA −12° was not significantly different between groups (Table 1). Table 1. ROM and MTC Stiffness in the Swimming and Volleyball Groups.

Swimming

Volleyball

ROM (°) 29.4 ± 10.4 20.7 ± 11.1 P<0.05

Stiffness (Nm/°)

MDA − 12° 0.84 ± 0.54 1.05 ± 0.94 n.s.

MDA − 8° 1.06 ± 0.46 1.24 ± 0.67 n.s.

MDA − 4° 1.29 ± 0.46 1.43 ± 0.58 n.s.

MDA 1.51 ± 0.55 1.62 ± 0.75 n.s.

Variables are represented as mean ± SD. Statistically significant differences between the swimming and volleyball groups are denoted by P<0.05. n.s. = indicates no significant difference. ROM = maximal dorsiflexion ankle angle, MTC = muscle-tendon complex

Jump Height Each jump height was significantly greater in the volleyball group than the swimming group (Table 2).

Table 2. Jump Height of Squat Jump (SJ), Countermovement Jump (CMJ), and Rebound Jump (RJ) in the Swimming and Volleyball Groups.

Swimming

Volleyball

Jump height (cm)

SJ 39 ± 7 45 ± 5 P<0.05

CMJ 42 ± 7 50 ± 5 P<0.01

RJ 36 ± 5 40 ± 6 P<0.05

Variables are represented as mean ± SD. Statistically significant differences between the swimming and volleyball groups are denoted by P<0.05 or P<0.01.

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Leg Strength Leg strength was calculated by dividing each of the measured values by the individual’s body mass. There were no significant differences between the swimming group and the volleyball group in extension-flexion strength of the right and left legs (Table 3). Table 3. Right- and Left-Leg Extension-Flexion Strength in Swimming and Volleyball Groups.

Swimming

Volleyball

Leg strength (Nm/ kg)

Right leg Extension 2.5 ± 0.6 2.8 ± 0.5 n.s.

Flexion 1.2 ± 0.3 1.4 ± 0.3 n.s.

Left leg Extension 2.4 ± 0.6 2.8 ± 0.6 n.s.

Flexion 1.2 ± 0.3 1.4 ± 0.3 n.s.

Variables are represented as mean ± SD. n.s. = no significant difference

Correlation There were significant correlations between RJ height and ATL, ATL/H ratio, and ATL/CPF ratio in the swimming group, but no significant correlations between morphometry parameters and jump height were found in the volleyball group (Tables 4 and 5). Table 4. Correlation of Squat Jump (SJ) Height, Counter Movement Jump (CMJ) Height, Rebound Jump (RJ) Height, and Measured Items in the Swimming Group.

SJ CMJ RJ Height 0.18 0.15 0.03

Body mass 0.14 0.14 −0.03

CPF 0.21 0.14 0.04

CPF/H 0.10 0.03 0.01

ATL 0.17 0.31 0.55*

ATL/H 0.09 0.24 0.52*

ATL/CPF 0.05 0.22 0.49*

ATT 0.13 0.03 −0.06

ROM 0.07 0.20 0.26

MTC stiffness

MDA − 12° −0.08 −0.03 −0.31

MDA − 8° −0.06 −0.05 −0.33

MDA − 4° −0.03 −0.05 −0.28

MDA 0.01 −0.05 −0.21

Leg strength

Right leg Extension 0.49* 0.60* 0.72**

Flexion 0.26 0.42 0.39

Left leg Extension 0.45 0.56* 0.64**

Flexion 0.38 0.46 0.44

SJ 1 0.92** 0.79**

CMJ --- 1 0.86**

RJ --- --- 1

Variables are represented as mean ± SD. Statistically significant differences are denoted by *P<0.05 or **P<0.01. CPF = the center of the popliteal fossa, CPF/H = ratio of the center of the popliteal fossa per height,

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ATL = Achilles tendon length, ATL/H = ratio of Achilles tendon length per height, ATL/CPF = ratio of Achilles tendon length per the center of the popliteal fossa, ATT = Achilles tendon thickness

There were no significant correlations between SJ and ATL/CPF ratio within the two groups combined, but there were significant correlations between CMJ or RJ (Figure 5) and ATL/CPF ratio within the two groups combined. There were no significant correlations between muscle-tendon complex stiffness and jump height in either group (Tables 4 and 5). There were significant correlations between right- and left-leg extension strength and jump height except between the left-leg extension strength and SJ height in the swimming group. Conversely, there was only a significant correlation between extension strength of the right leg and CMJ height in the volleyball group (Tables 4 and 5).

Figure 5. Scatter Plot of the Rebound Jump (RJ) Height and Tendon Length Ratio for the

Swimming and Volleyball Groups. O = swimming group, ◆ = volleyball group, ATL/CPF = ratio of

Achilles tendon length per the center of the popliteal fossa

Table 5. Correlation of Squat Jump (SJ) Height, Counter Movement Jump (CMJ) Height, Rebound Jump (RJ) Height, and Measured Items in the Volleyball Group.

SJ CMJ RJ Height −0.01 −0.27 0.04

Body mass −0.08 −0.36 −0.24

CPF −0.02 −0.15 0.00

CPF/H −0.02 0.07 −0.03

ATL −0.18 0.03 0.10

ATL/H −0.19 0.13 0.09

ATL/CPF −0.24 0.12 −0.11

ATT 0.10 0.21 −0.23

ROM 0.06 0.03 0.12

MTC stiffness

MDA − 12° 0.08 −0.11 0.18

MDA − 8° −0.07 −0.23 0.10

MDA − 4° −0.30 −0.35 −0.07

MDA −0.40 −0.34 −0.19

Leg strength

Right leg Extension 0.01 0.12 −0.11

0

10

20

30

40

50

60

35.0 45.0 55.0

RJ

heig

ht

(cm

)

ATL/ CPF(%)

r = 0.451 (p < 0.01)

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Flexion −0.11 0.27 0.01

Left leg Extension 0.06 0.51* −0.14

Flexion −0.07 0.22 −0.14

SJ 1 0.47 0.09

CMJ --- 1 0.09

RJ --- --- 1

Variables are represented as mean ± SD. Statistically significant differences are denoted by *P<0.05 or **P<0.01. CPF = the center of the popliteal fossa, CPF/H = ratio of the center of the popliteal fossa per height, ATL = Achilles tendon length, ATL/H = ratio of Achilles tendon length per height, ATL/CPF = ratio of Achilles tendon length per the center of the popliteal fossa, ATT = Achilles tendon thickness

DISCUSSION In this study, we measured the morphological characteristics of the AT, the mechanical properties of the muscle-tendon complex of the ankle flexor, leg strength, and jump ability in male university swimmers and volleyball players. In additional to comparing adaptation to different types of long-term physical training, we examined the differences in how these significant factors correlated with jump ability for the two groups. Our results showed that the mechanical properties of the muscle-tendon complex of the ankle flexor and leg strength were not different between groups, although jump ability was significantly greater in the volleyball group than in the swimming group. In addition, the volleyball group had greater average ATL and ATT compared with the swimming group. The ATL was one of the factors that correlated with RJ capacity in the swimming group but not in the volleyball group. Based on these results, the morphology of the AT may change because of long-term training in accordance with the playing characteristics of the sport. Height, Body Mass, and Morphometry of AT Although we found a significant difference in the ATL ratio between the different athletes, this finding was not always consistent with that of previous studies. For example, Kongsgaard et al. (6) reported that the ATL ratio was not significantly different among long-distance runners, volleyball players, and kayakers. To our understanding, no studies have focused on swimmers’ ATL. The swimmers who participated in the present study did not have intensive jump experience (i.e., characterized by quick stretch shortening cycles and body-weight resistance) because their routine training occurs in a setting with water buoyancy. Therefore, a significantly different ATL ratio could be expected between the swimmers and the volleyball players, who use quick SSC operations routinely. However, the ATL ratio was not changed in the intervention study (5). Thus, long training period may be required to change the ATL ratio. Fouré and colleagues (3) suggested that the ATL ratio is associated with jump performance. In this study, ATL was significant correlated with some jump performance parameters in the swimming group or the combined group; whereas, the ATL was not correlated with jump performance in the volleyball group alone. This interesting result may indicate that both ATL ratio and jump performance increase during jump training, although the increase of the ATL may reach a limit. The ATT of the volleyball group in this study showed a significantly higher value than that of the swimming group. This result is supported by several previous studies. In the study by Kongsgaard et al. (6), the CSA of the AT measured by MRI was significantly greater in the

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volleyball players than in the long-distance runners, and kayak athletes. They concluded that large intermittent load to AT accompanied by the routine movement of volleyball players enlarged the CSA. Also, in the study by Magnusson (12), who compared the CSA of the AT measured by MRI of runners and non-runners, the CSA of the AT in runners was significantly greater at 10, 20, 30, and 40 mm from the calcaneus stop of the AT compared with non-runners. These results indicate that the CSA of the AT is enlarged by the larger exercise loads over a long period. In the present study, we measured the ATT by ultrasound, and it was significantly greater in the volleyball group than in the swimming group. Measurement by ultrasound is considered to have reduced accuracy compared with measurements by MRI. However, the coefficient of variation (CV) of the ATL measurement was 4.0% and the CV of the ATT measurement was 1.1% during this study. Therefore, we think we were able to evaluate the morphology of the AT reasonably well by ultrasound. ROM and Mechanical Properties of the Ankle Joint In the present study, ROM was significantly greater in the swimming group. However, there were no significant differences between groups in the stiffness of the muscle-tendon complex of the ankle flexor. In addition, there was no significant correlation between the ROM or stiffness and jump height in either group. In previous studies, there was no consensus about whether the stiffness of the ankle joint or tendon was correlated to jump ability. In the cross-sectional study of Møller et al. (13), there was significant correlation between the stiffness of the tendon of the vastus lateralis muscle, measured in voluntary muscle isometric contraction, and SJ or CMJ height. In contrast, in the cross-sectional study of Kubo et al. (10), there was no significant correlation between ankle stiffness and SJ, CMJ, or RJ heights, nor a correlation between AT stiffness and CMJ or drop jump heights. We measured the ankle joint stiffness in passive dorsiflexion to avoid voluntary muscle isometric contraction associated with optional effort. As a result, the measured values were not a factor in determining the jump ability. Leg Strength There were no significant differences between the groups in leg strength. There was a significant correlation between right- and left-leg extension strength and jump height in the swimming group, while no significant correlation existed between leg extension strength and jump height in the volleyball group, except between left-leg strength and CMJ height. In Sheppard’s study (15), when measured in men’s volleyball players, a significant correlation between relative CMJ height (absolute jump height (cm) -standing reach height (cm) = relative jump height) and peak power per unit body weight existed. In addition, in the Nuzzo et al. study (11) involving football players and track-and-field athletes, there were significant correlations between squat (1 repetition maximum per body weight) and CMJ height, peak power of CMJ, and peak velocity. Thus, leg extension strength may be a factor related to jump performance. However, the higher correlations between leg strength and jump performance observed in the swimming group may suggest that if an athlete is trained in jumping daily like volleyball players, the contribution of the lower-limb muscle strength to jump performance is decreased.

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CONCLUSIONS

The male university volleyball players have a longer and thicker AT compared with male university swimmers. Thus, different types of exercise training over a long period can affect the morphology of the AT as well as factors correlated with jump performance.

ACKNOWLEDGMENTS

We appreciate his participation and parents of the minority who admitted participation in this study. Address for correspondence: Mami Yoshimura, Laboratory for Exercise Physiology and Biomechanics, Graduate School of Health and Sport Sciences, Chukyo University, 101 Tokodachi, Kaizu-cho, Toyota, Aichi, Japan, 470-0393, Email: dd.gw2.39@gmail.com REFERENCES

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