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J Exerc Rehabil > Volume 12(5);2016 > Article
Kim and Jeoung: Assessment of isokinetic muscle function in Korea male volleyball athletes

Abstract

Volleyball players performed numerous repetitions of spike actions, which uses and requires strong and explosive force, and control of the muscles of the shoulder, lower back, and legs. Muscle imbalance is one of the main causes of sport injuries. The purpose of this study was to assess isokinetic muscle functions in male volleyball players. We thus aim to accurately evaluate their muscle functions, and identify the best training strategy to achieve optimal muscle strength balance in future training programs. The participants in this study consisted of 14 male volleyball players. Muscle strength was measured using the isokinetic dynamometer. Muscle strength was evaluated in terms of peak torque and average power, calculated from five repeated measurements at an angular speed of 60°/sec. Three players who were left attackers showed shoulder imbalance, four players showed trunk joint imbalance, nine players had knee joint of extension/flexion imbalance and four players showed left/right imbalance. The results showed that the number of volleyball players with differences between the strength of the bilateral knee muscles, and between the strength of the hamstrings and quadriceps muscles was higher than the number of players with differences between the strength of the shoulder internal and external rotation muscles, and higher than the number of players with differences between the strength of the lower back extension and flexion muscles.

INTRODUCTION

Volleyball is a sport played in a relatively small court (9 m×9 m), inside which the players perform fast movement and repeated high vertical jumping in a very short time. During a volleyball match, the players are required to serve, pass, and set the ball, as well as to spike and attack. Among those actions, spiking and attacking demand intense vertical jumping and landing.
During volleyball matches, when numerous repetitions of the aforementioned movements are performed, the anaerobic type of exercise is the most frequently performed activity, with a ratio to aerobic exercises of 7:3 (Lamb, 1984). Playing volleyball also requires agility and fast reaction time in order to prevent the ball from touching the floor. A good muscle strength ratio between dominant and nondominant sides, and between antagonist and agonist muscles, especially of the knee joint, is ultimately important for sports in order to have stability of the lower limbs and to prevent knee injury (Agaard et al., 1998; Bahr and Krosshang, 2005). Since muscle imbalance is one of the main causes of sport injuries, the assessment of the muscle function is very important for designing injury prevention programs.
The hamstrings (flexion) and the quadriceps femoris (extension) muscles are the key effectors during high performance activities during sports, such as running and jumping (Jespersen et al., 2000). Most of the lower limb movements require strong bilateral muscle contractions (MacLaren, 1990). For volleyball it is important to have balanced muscle strength development in both legs (Brooks and Fahey, 1987; Thorstensson et al., 1976), with minimal differences regarding muscle strength between the dominant and nondominant legs. Further, the ratio between the muscle strengths of the hamstring and of the quadriceps (H/Q) should be low for volleyball.
Moreover, during a spike action, the muscles of the legs, lower back, and knees are used in an explosive manner in order to generate a strong force, which requires effective control of the entire body in order to prevent injury. In other words, an ideal training method for volleyball would have to train the simultaneous control of the lower back, knees, and legs.
As it was previously reported, the spike and serving motions of volleyball require such dynamic stabilization in order to maintain the integrity of the glenohumeral joint (Aagaard and Jørgensen, 1996; Bahr and Krosshang, 2005). Stability of the glenohumeral joint during the acceleration, deceleration, and follow-through phases of striking is maintained by the rotator cuff muscles acting eccentrically, compressing the humeral head. Thus, active and passive mechanisms work to maintain dynamic stability and compression of the humeral head within the glenoid fossa during spiking and serving. A study by Aagaard et al. (1997) investigated knee injury in 295 Danish volleyball players and found that 55% of the players had experienced knee injury at least once, while 48% responded as having chronic knee injury. Players with 11.5 years of experience are in a group with increased risk of overuse injuries (Seminati and Minetti, 2013).
Further, a previous study showed that, for achieving good performances during powerful spikes and servings, cooperative harmony between the hamstrings, quadriceps, shoulder, and lower back muscles (Chung et al., 1987; Han et al., 2011). Specially, volleyball attackers exhibit increased risk for back injuries due to increased spinal twisting, flexing, lateral bending, and asymmetrical movements. In general, low back injuries are associated with dysfunctions regarding trunk muscle coactivation or recruitment patterns, not with reduced strength (Seminati and Minetti, 2013).
Isokinetic assessment can be used to measure torque values at several joint of the body. This assessment typically involves comparing the joint of interest with the corresponding contralateral joint. Isokinetic testing evaluates the torque generated during the exercise, allowing for an assessment of strength and functional ability, for a comparison of different muscles.
The objective of the present study was to assess isokinetic muscle functions in male volleyball players of the Korean national volleyball who is preparing for the 2020 Tokyo Olympics. We thus aim to accurately evaluate their muscle functions, and identify the best training strategy to achieve optimal muscle strength balance in future training programs.

MATERIALS AND METHODS

Participants

The participants in the present study consisted of 14 male volleyball players, aged 16–26 years, who are members of the Korean national volleyball team preparing for the Tokyo Olympics in 2020. The participants self-reported their play position, dominant leg and shoulder, length of their volleyball career, and age. Anthropometric measurements (Table 1) included height, body weight (BW), muscle mass, and body composition, and were performed using Inbody2 (Inbody 670, Seoul, Korea). The mean volleyball playing experience among the study participants was 103.14±39.6 months (range, 17–148 months). The mean height, weight, and age were 193.69±7.6 cm (range, 182.9–207.8 cm), 84.76±7.47 kg (range, 76.3–100 kg), and 20.7±1.8 years (range, 18–25 years), respectively.
All participants had previously undergone isokinetic testing. They had no history of surgery of the knee, shoulder, or trunk. All measurements were taken regardless of injury status. Before testing, the participants completed a nonspecific, 5-min warm-up on a stationary bicycle ergometer at a self-regulated, low-to-moderate intensity, followed by 10 min of dynamic stretching that targeted the main muscle group being tested. The warm-up routine was performed under the supervision of a examiner.

Procedures

In the present study, muscle strength was measured using the isokinetic dynamometer (Cybex International Inc., New York, NY, USA) at the Department of Exercise Rehabilitation and Welfare, Gachon University. All measurements were performed by a examiner with 5 years of experience, during a single test session. Muscle strength was evaluated in terms of peak torque and average power, calculated from five repeated measurements at an angular speed of 60°/sec. To allow comparisons in terms of maximum muscle strength in the shoulder, knee, and lumbar joints, the peak torque was normalized by BW (PTBW, percent of torque produced per kg of BW).
Muscle strength in the shoulder was measured on the dominant side, while the shoulder’s internal rotation and external rotation (peak torque, expressed in units of Nm) were measured for the striking arm, i.e., the shoulder that the participant reported to be using most frequently for hitting or serving the ball during the game (Stickley et al., 2008). The measurements were taken with the participants in a seated modified neutral position, with 90° of elbow flexion, 30° of glenohumeral joint flexion, and 30° of glenohumeral abduction; during the measurements, the participants wore stabilization straps across the hip and upper body.
The H/Q ratios for the right and left knee were measured on an adjustable dynamometer chair, with the participants comfortably seated with the hip joint at approximately 75° of flexion (where 0° represents full extension). The participants wore straps, and the shoulders were fixed in ventral-dorsal and cranial-caudal direction using shoulder pads. For further stabilization of the upper body during the test session, the participants were instructed to hold the handgrips located on the side of the chair. The measurement was taken with the participants performing concentric flexion and extension with their knees.
Trunk strength was measured between the 4th and 5th lumbar vertebrae, where the extension of the iliac crest meets the spine. Using this position as the reference, the footplate of the isokinetic dynamometer was adjusted to accommodate comfortable depth and height for each participant. The participants stood on the footplate, and pads were placed and fixed on the chest (below the clavicle), thighs, and below the knees. Subsequently, the participants were instructed to hold both handgrips located in front of their chest. The dynamometer used in our study was designed to enable trunk flexion and extension movements in an up-right position, with the feet positioned on two horizontal footplates, and the knees in a slightly flexed position (10°–20°). We measured trunk strength during trunk flexion from −10° to 50°, and during trunk extension from 50° to −10° (Davies and Gould, 1982; Guilhem et al., 2014).

Data analysis

The raw data for assessment and diagnosis of isokinetics and function of the shoulders, lower back, and knees were organized using Excel 2010 (Microsoft Corp., Redmond, WA, USA). The results are given as mean±standard deviation and range.

RESULTS

Tables 2, 3, and 4 show the results regarding muscle strength of the shoulders, knees, and lower back in members of the male Korean national volleyball team preparing for the Tokyo Olympics in 2020.
With respect to the isokinetic muscle function in the shoulder, the lowest PTBW was noted for the athletes with the shortest volleyball experience (PTBW was 101 and 104 Nm/kg for participants V10 and V14, respectively), while the highest PTBW (149 Nm/kg) was noted for participant V13. When considering the playing position, the participants with highest PTBW values were V13 (PTBW=143 Nm/kg), V12 (PTBW=116 Nm/kg), and V8 (PTBW=134 Nm/kg) for the left, center, and right position, respectively, while participant V7 had the highest PTBW (137 Nm/kg) among setters and libero players. Therefore, playing in the left position was associated with the highest PTBW of the shoulder, while playing in the center position was associated with the lowest PTBW. Participant V1 exhibited a low ratio (31%) between internal and external rotation of the shoulder, while participants V3 and V14 exhibited a high ratio (75% and 69%, respectively), suggesting muscle imbalance. Among these, only participant V3 reported having shoulder injury and associated shoulder pain.
With respect to the isokinetic muscle function in the lumbar joints, participant V4 had the lowest power (PTBW=301 Nm/kg), while participant V4 had the highest power (PTBW=468 Nm/kg). When considering the playing position, the participants with the highest PTBW were V4 (PTBW=468 Nm/kg), V8 (PTBW=456 Nm/kg), and V10 (PTBW=402 Nm/kg) for the left, right, and center position, respectively, while participant V6 had the highest PTBW among setters and libero players (PTBW= 447 Nm/kg). Therefore, playing in the left position was associated with the highest PTBW of the lumbar joints, while playing in the center position was associated with the lowest PTBW. A total of 4 out of 14 participants (V4, V5, V8, and V11) exhibited a low ratio (<80%) of extension and flexion in the lower back, suggesting muscle imbalance.
With respect to isokinetic muscle function in the knee, we found that the PTBW was generally higher in the right knee than in the left. Participant V4 had the highest PTBW (378 Nm/kg) of the right knee, while participant V10 had the lowest PTBV (148 Nm/kg). When considering the playing position, the participants with the highest PTBW were V4 (PTBW=378 Nm/kg), V8 (PTBW=313 Nm/kg), and V12 (PTBW=250 Nm/kg) for the left, right, and center position, respectively, while participant V7 had the highest PTBW among setters and libero players (PTBW= 319 Nm/kg). Therefore, playing in the left position was associated with the highest PTBW, while playing in the center position was associated with the lowest PTBW.
Of the 14 participants, a total of 8 (V1, V2, V4, V5, V10, V12, V13, and V14) had left-right extension deviation of >10%, while 4 (V1, V4, V7, and V13) had left-right flexion deviation. Moreover, considering that the normal extension and flexion ratio is 50%–70%, a total of 4 participants (V1, V5, V10, and V11), showed imbalance on the right side, while 5 participants (V1, V2, V5, V11, and V14) showed imbalance on the left side. Among these, there were two participants with PTBW of <200 Nm/kg, specifically: participant V10 among center position players (PTBW=149 Nm/kg), and participant V1 among left position players (PTBW=188 Nm/kg).

DISCUSSION

Assessments of muscle strength have been conducted using various isometric, isotonic, and isokinetic exercise methods. It was suggested that isokinetic exercise using an isokinetic dynamometer allows for a more objective and accurate assessment (Hislop and Perrine, 1967) this was later proven by Thistle et al. (1967). During isokinetic exercise, which has a predefined exercise speed, when the muscle strength is too high, or the exercise speed exceeds the limit predefined in the machine, the machine applies a resistance force equivalent to the surpassing amount. This resistance force is considered to expresses the force generated in the muscles, and is stored in the machine as torque force. Moreover, unlike isometric or isotonic exercises, the isokinetic exercise has the advantage of generating maximum contraction for the entire range of motion (ROM) (Hislop and Perrine, 1967). Thus, isokinetic exercise can objectively and accurately compare the bilateral muscle strengths of a particular joint, as well as the agonistic and antagonistic muscle strengths of a single joint. Further, this technique also allows for evaluating the strength in relation to BW. Moreover, the exercise speed can be increased as the muscle strength increases in order to allow for a gradually increasing intensity during exercise and training (Gilliam et al., 1979; James et al., 2014; Kim and Youn, 2005; Rodríguez-Ruiz et al., 2014; Rosene et al., 2001).
The optimal ratio between internal and external rotation in the shoulder was shown to be 3:2; the optimal ration between trunk flexion and extension was shown to be 1:1; and the optimal ratio between knee flexion and extension was shown to be 2:3 (Dvir, 2004; Rosene et al., 2001). However, the ranges of ideal muscle strength ratio vary depending on the study. For the knees, the ratio of forces involved in extension to those involved in flexion should be at least 50%–70%. Further, the force ratio between the dominant and nondominant sides should be of 1:1; however, a difference of 10% is considered as being within a normal range (Andrade Mdos et al., 2012; Cheung et al., 2012; Dirnberger et al., 2012; Elliott, 1978).
ROM used during trunk isokinetic testing varies depending on the study. Smith et al. (1985) used flexion range of 30°–40° and extension range of 15°–20°, while Kim and Shin (1999) and Newton et al. (1993) applied flexion range of 80°, and Davies and Gould (1982) applied a ROM of ≥90°. However, the most effective ROM for studying trunk muscle strength and trunk exercise has not been suggested yet. In the present study, ROM was set to 80° for flexion and 15° for extension, in order to induce peak isokinetic flexion and extension. All participants were able to perform the exercise relatively easily within these ranges. The angular speed used to measure trunk isokinetic strength depends on the study. Particularly, with respect to the speed of isokinetic trunk flexion and extension, Parnianpour et al. (1988) stated that trunk flexion and extension speed of 60°/sec is appropriate for activities of daily living, while a speed of 30°/sec is appropriate for patients with lower back pain (Marras and Wongsam, 1986); if lower back injury is incomplete, measuring at 60°/sec would not represent a fully functional activity. Newton et al. (1993) stated that the ideal measurement should account for the exercise speeds of 60°/sec, 90°/sec, and 120°/sec. In the present study, the speed was set to 60°/sec for measuring the maximum muscle strength of the volleyball players.
There have been many studies on the extension and flexion strength of the trunk muscles, and the reported results have indicated that extension was stronger than flexion (Flint, 1958; Guilhem et al, 2014; Mayer et al., 1985; McNeill et al., 1980; Smidt et al., 1980). The reason for this is that the cross section during trunk extension is bigger than during flexion. Therefore, although the trunk extension to flexion ratio is known to be from 1.1:1 to 2.7:1 (Dvir, 2004; Smith et al., 1985; Wessel et al., 1992), in the case of volleyball players, at the moment of bending the lower back backwards and engaging in position for spiking or serving, maximum power is generated by the combination of power from flexion motion of the lower back and of the shoulders. Therefore, it would be possible to assume that the appropriate flexion to extension ratio for preventing lower back injury and for drawing out peak sports performance would be 1:1. However, the results of the present study showed that 13 of the 14 players exhibited greater strength for extension than for flexion. Moreover, results from measurements of 5 repetitions performed at the speed of 60°/sec showed that 4 of the 14 players had a difference of ≥20% in the trunk flexion-to-extension ratio, showing a relative imbalance regarding the strengths for extension and flexion. This result supports the need for training programs focused on balance control. In order to understand which ratios would allow for better spike and serving skills during matches, studies on reference values for PTBW and extension and flexion strength ratio are needed. Most volleyball players use one arm the dominant to practice a lot of forceful spike and overhead serves during the training season.
Bahr and Krosshaug (2005) indicated that muscle imbalance causes damages to the joints by pulling down on the joints in an asymmetric manner (Meister and Andrews, 1993). Based on this, it is possible that having unbalanced internal to external rotation ratios is associated with higher risk of injury. Chung et al. (1987) compared the external and internal rotation muscle strengths of healthy Korean adults and found that the muscles responsible for internal rotation had higher strength than those responsible for external rotation. The results of Mayer et al. (1994) indicated that normal ratios of external to internal rotation strengths for the general population for 60°/sec testing were 0.57 for the dominant side and 0.61 for the nondominant side in a concentric test. Wang et al. (2000) measured shoulder muscle strength of players on the English national volleyball team and found that the ratio of strength of the external rotator to that of the internal rotator muscle were approximately 1 for the dominant side and 0.67 for the non-dominant side in a concentric test.
In the present study, the difference in shoulder internal and external rotation ratio was 53.2%, with internal rotation showing. Imbalance in shoulder internal-to-external rotation strength ratio was observed in 3 of the 14 players. In the results of the present study and in those of precedent studies, internal-to-external rotation strength ratios of volleyball players’ shoulders were 3:2 for the dominant side, but 1:1 for the nondominant side. Accordingly, studies regarding internal and external rotation ratios are warranted in order to facilitate the prevention of shoulder injuries. Further, such studies, when focused on game performance, could help identify the minimal value of PTBW required for performing volleyball actions such as powerful spike and serving (James et al., 2014; Wang et al., 2000).
The major agonistic muscles recruited for those movements are the hamstrings and the quadriceps, with the back of the legs and the tibialis anterior also serving as contributors. Moreover, for spike actions, a greater coordination between the major back muscles and the muscles of the shoulder area must be achieved (Reeser et al., 2006; Seminati and Minetti, 2013)
Imbalance signifies possible additional risk, such as soft tissue damage, regardless of the various causes of injury (Zakas et al., 1995). Of course, there are limitations in relating the isokinetic muscle strength, measured mechanically, to the possibility of injury in an actual match or during practice situations. However, in the field of sports medicine, this relation is commonly very high. In particular, Aagaard et al. (1998) claimed that having an isokinetic muscle strength ratio of ≤60% at low angular speed increased the risk of injury, while Ayala et al. (2012) reported that increased quadriceps strength from training can reduce activation of antagonistic muscles of the hamstrings. Such low isokinetic balance ratio can be a cause of increased risk of knee injury by exerting tensional stress on the anterior cruciate ligament due to a decrease in joint stabilizing muscle strength (Cheung et al., 2012; Rosen et al., 2001).
Three out of 14 players had a shoulder flexion-to-extension ratio of 2:3. When considering the knees, shoulders, and lower back, the region for which the highest number of players exhibited imbalance was the knee joints. Players of the left position exhibited the highest peak torque values for the shoulders, knees, and lower back, while players of the center position exhibited the lowest peak torque for all regions. In a study by Chae et al. (2002), the mean knee kinetic 60°/sec PTBW of volleyball players who play on attacking positions was 329, while those of setters and libero players were 310 and 314, respectively. However, in the present study, left side attackers exhibited a PTBW of 291, while the highest value of PTBW was 378, for the participant V4, which indicates significant variation among attackers.
In a study by Kim and Choi (2007), the national team players showed normal reference values, with a PTBW of 270, left-right deviation of <10%, and an extension/flexion ratio of 55%. In the present study, 8 out of 14 participants had left-right deviation ≥10%, while 4 out of 14 had muscle imbalance (i.e., an extension/flexion ratio outside the range 50%–70%). We may conclude that the volleyball players included in the present study should undergo a rehabilitation program to recover from knee injury.
Participating in elite sports competitions requires continuous, quantitative improvement in the angular torque and angle for which maximum muscle strength is manifested, as these parameters allow superior execution of actions during which maximum muscle strength needs to be generated quickly. The underlying mechanisms were proposed by Thorstensson et al. (1976), and involve force, muscle contraction speed, and muscle fiber relationships. Specifically, the maximum force generated depends on the number and type of muscle fibers recruited, as well as on the speed and cooperativity of nerve impulses. Moreover, recruitment of the nerve-muscle unit is very important for increasing the efficiency of movement, and this is reported to be highly associated with the angle at which maximum muscle strength is manifested (Moffroid et al, 1969). Taken together, these results suggest that the angle at which maximum muscle strength is manifested plays a very important role in sports performance. Together with maximum muscle strength, this angle affects mean power and muscle endurance. Since power represents the value of work divided by time, muscle strength (i.e., force) must be increased above all others, and must be generated in the initial stage of the effort in order to achieve increased power. In the present study, an isokinetic dynamometer was used to assess the shoulder, lower back, and knee muscle functions of male players of the Korean national volleyball team. The results showed that the number of volleyball players with differences between the strength of the bilateral knee muscles, and between the strength of the hamstrings and quadriceps muscles was higher than the number of players with differences between the strength of the shoulder internal and external rotation muscles, and higher than the number of players with differences between the strength of the lower back extension and flexion muscles. These findings may suggest that the risk of knee injury is greater than that of shoulder or lower back injury. With respect to player positions, players who play in the center position exhibited the lowest muscle function for all the 3 studied categories (shoulders, knees, and lower back). Future studies are warranted to research the reference values of optimal PTBW, which can be used for injury prevention and for executing powerful spikes and servings.

Notes

CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

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Table 1
Baseline characteristics of the study participants (n=14)
No. Height (cm) Weight (kg) Experience (mo) Position
V1 192.2 85.2 120 L
V2 200 87.7 86 L
V3 186 84.5 96 L
V4 188 76.3 69 L
V5 191 82.3 122 R
V6 182.9 78.2 135 Li
V7 186.4 76.5 150 S
V8 194.8 85 125 R
V9 188.3 77.9 136 S
V10 201.9 100 41 C
V11 188.3 83.3 137 L
V12 207.8 99.8 84 C
V13 199.8 85.4 120 L
V14 203.2 82.6 17 L
Mean±SD 193.69±7.6 84.76±8.09 103.14±39.6

The volleyball players’ position codes are: C, center; L, left; Li, libero; R, right; S, setter.

V, volleyball player; SD, standard deviation.

Table 2
Shoulder joint isokinetic muscle function assessment
Player’s position Rotation Peak torque (Nm) Peak torque/% BW (Nm/kg) Average power per repetition (Nm) Average power per repetition/% BW (Nm/kg)
V1 (L) Internal rotation 114 137 90 108
External rotation 35 42 23 29
Ratio 31 26

V2 (L) Internal rotation 111 125 89 99
External rotation 54 60 42 46
Ratio 49 47

V3 (L) Internal rotation 98 116 79 92
External rotation 73 86 51 59
Ratio 75 65

V4 (L) Internal rotation 95 122 80 103
External rotation 52 66 40 53
Ratio 54 50

V5 (R) Internal rotation 107 131 90 110
External rotation 58 72 38 46
Ratio 54 42

V6 (Li) Internal rotation 100 128 87 112
External rotation 58 75 44 57
Ratio 58 51

V7 (S) Internal rotation 104 137 80 103
External rotation 54 72 43 55
Ratio 52 54

V8 (R) Internal rotation 113 134 92 110
External rotation 66 77 57 68
Ratio 59 62

V9 (S) Internal rotation 96 125 77 99
External rotation 50 66 35 44
Ratio 52 45

V10 (C) Internal rotation 100 101 79 81
External rotation 50 51 32 33
Ratio 50 41

V11 (L) Internal rotation 118 143 92 112
External rotation 61 75 38 46
Ratio 52 41

V12 (C) Internal rotation 117 116 96 97
External rotation 62 63 43 44
Ratio 53 45

V13 (L) Internal rotation 127 149 101 119
External rotation 57 66 42 48
Ratio 45 42

V14 (L) Internal rotation 87 104 69 81
External rotation 60 72 45 53
Ratio 69 65

Total (mean) Internal rotation 99.8 126.2 85.8 101.9
External rotation 56.4 67 40.92 48.6
Ratio 53.2 47.8

The volleyball players’ position codes are: C, center; L, left; R, right; S, setter.

BW, body weight; V, volleyball player.

Table 3
Knee joint isokinetic muscle function assessment
Player’s position Imbalance Peak torque (Nm) PT/%BW (Nm/kg) Average power per repetition (Nm) APR/%BW (Nm/kg)




R L Ratio R L R L Ratio R L
V1 (L) EX 155 89 57 188 107 104 61 60 125 75
FLEX 122 107 88 146 128 91 80 89 110 97
Ratio 79 120 - 77.6 119 88 131 - 88 129

V2 (L) EX 205 156 76 229 176 126 103 82 141 116
FLEX 140 129 92 158 143 105 91 87 119 101
Ratio 68 83 - 69 81.2 83 88 - 84.4 87

V3 (L) EX 235 240 98 277 283 138 152 91 163 180
FLEX 134 137 99 158 161 92 98 94 108 116
Ratio 57 57 - 56.6 57 67 64 - 66.2 64

V4 (L) EX 290 217 75 378 283 193 147 76 251 191
FLEX 186 145 78 241 188 126 106 84 165 138
Ratio 64 67 - 64 66.4 65 72 - 66 72

V5 (R) EX 217 119 55 265 146 146 92 63 178 112
FLEX 170 153 90 206 188 120 110 92 147 134
Ratio 78 128 - 78 128 82 120 - 83 119

V6 (Li) EX 241 217 90 310 280 171 150 68 220 193
FLEX 159 144 90 203 185 117 109 93 149 141
Ratio 66 66 - 65 66 73 73 - 68 73

V7 (S) EX 245 224 91 319 292 165 138 84 215 180
FLEX 125 142 88 161 185 94 102 92 123 132
Ratio 51 64 - 50.4 63.3 57 74 - 57 73

V8 (R) EX 264 283 94 313 337 171 183 93 202 218
FLEX 182 174 96 215 206 114 115 99 136 136
Ratio 69 61 - 69 61 67 63 - 67 62

V9 (S) EX 195 201 97 250 259 122 144 85 156 185
FLEX 132 136 97 170 173 97 92 95 125 119
Ratio 67 68 - 68 67 80 64 - 80.1 64

V10 (C) EX 146 209 70 149 215 82 112 73 84 114
FLEX 122 118 97 125 119 75 76 99 77 77
Ratio 83 56 - 84 55 91 65 - 92 68

V11 (L) EX 274 256 93 331 310 186 154 83 224 187
FLEX 129 125 97 155 152 91 85 93 110 103
Ratio 47 49 - 47 49 49 55 - 49 55

V12 (C) EX 250 206 82 250 209 170 149 88 171 149
FLEX 151 136 90 152 137 102 98 96 103 99
Ratio 60 66 - 61 66 60 66 - 60 66

V13 (L) EX 285 220 77 334 259 210 149 71 246 176
FLEX 151 129 85 176 152 105 94 90 123 110
Ratio 53 59 - 53 59 50 63 - 50 63

V14 (L) EX 252 202 80 301 241 178 145 81 211 171
FLEX 165 152 92 197 182 120 115 96 143 136
Ratio 66 75 - 65 81 67 79 - 68 80

Total (mean) EX 232.4 196.4 84.5 278.1 242.6 154.4 134.2 78.4 184.7 160.5
FLEX 147.7 137.6 93.1 175.9 164.2 103.5 90.3 92.7 124.1 117
Ratio 64.8 72.7 - 64.8 72.7 69.9 76.9 - 69.9 76.7

The volleyball players’ position codes are: C, center; L, left; R, right; S, setter.

BW, body weight; EX, extension; FLEX, flexion.

Table 4
Trunk joint isokinetic muscle function assessment:
Player’s position Imbalance Peak torque (Nm) Peak torque/% BW (Nm/kg) Average power per repetition (Nm) Average power per repetition/% BW (Nm/kg)
V1 (L) EX 335 405 218 264
FLEX 358 432 288 347
Ratio 106 7

V2 (L) EX 344 387 265 297
FLEX 311 349 253 284
Ratio 90 95

V3 (L) EX 296 349 228 270
FLEX 282 334 232 275
Ratio 95 98

V4 (L) EX 359 468 272 354
FLEX 248 322 220 286
Ratio 69 81

V5 (R) EX 317 384 251 303
FLEX 228 274 180 218
Ratio 72 72

V6 (Li) EX 347 447 235 325
FLEX 293 376 235 301
Ratio 84 93

V7 (S) EX 328 426 240 312
FLEX 296 384 244 316
Ratio 90 98

V8 (R) EX 384 456 232 275
FLEX 273 325 226 268
Ratio 71 97

V9 (S) EX 343 441 238 305
FLEX 283 364 237 305
Ratio 83 100

V10 (C) EX 395 402 231 235
FLEX 389 396 285 292
Ratio 99 81

V11 (L) EX 344 447 236 308
FLEX 256 334 220 286
Ratio 74 93

V12 (C) EX 382 384 278 281
FLEX 366 370 300 303
Ratio 96 93

V13 (L) EX 287 337 222 262
FLEX 296 349 232 273
Ratio 97 96

V14 (L) EX 252 301 201 240
FLEX 292 346 223 266
Ratio 86 90

Total (mean) EX 339.5 402.4 239 287.9
FLEX 297.9 353.9 241 287.7
Ratio 85.7 90.1

The volleyball players’ position codes are: C, center; L, left; R, right; S, setter.

BW, Body weight; EX, extension; FLEX, flexion.

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