Changes in lower extremity function and pitching performance with increasing numbers of pitches in baseball pitchers

Article information

J Exerc Rehabil Vol. 14, No. 3, 430-435, June, 2018

Publication date (electronic) : 2018 June 27

doi : https://doi.org/10.12965/jer.1836196.098

Osamu Yanagisawa, Hidenori Taniguchi

Faculty of Business Information Sciences, Jobu University, Isesaki, Japan

^*Corresponding author: Osamu Yanagisawa, https://orcid.org/0000-0001-8125-7833, Faculty of Business Information Sciences, Jobu University, 634-1, Toyazuka-machi, Isesaki, Gunma 372-8588, Japan, Tel: +81-270-32-1011, Fax: +81-270-32-1126, E-mail: yanagisawa@ic.jobu.ac.jp

Received 2018 April 5; Accepted 2018 April 19.

Abstract

INTRODUCTION

Ball velocity and pitching accuracy are determining factors that strongly influence pitching performance for baseball pitchers. Several studies demonstrated a close correlation between ball velocity and ground-reaction force generated during pitching (Guido and Werner, 2012; MacWilliams et al., 1998). Therefore, greater force and power generated from the lower extremities is thought to be significant for increasing ball velocity in baseball pitching (Guido and Werner, 2012; Kageyama et al., 2014; Kageyama et al., 2015; MacWilliams et al., 1998). In addition, a stable base of the lower extremities should contribute to enhancement of pitching accuracy by supporting the powerful motions of the trunk and upper extremities (Fortenbaugh et al., 2009; Kageyama et al., 2014; Kageyama et al., 2015; Marsh et al., 2004; Milewski et al., 2012). Moreover, it is important for baseball pitchers to keep lower extremity function at a high level throughout the course of a baseball game for better pitching performance.

Several previous studies (Escamilla et al., 2007; Grantham et al., 2014; Murray et al., 2001) have investigated changes in biomechanical parameters of the lower extremities during pitching and ball velocity with increasing numbers of pitches in baseball pitchers. Murray et al. (2001) showed significant decreases in knee angle at ball release and ball velocity at the last inning of a simulated game in professional baseball pitchers. These findings might have resulted from muscle fatigue of the lower extremities due to repetitive pitching motions. Although Mullaney et al. (2005) found minimal muscle fatigue in the hip musculature after pitching 7±2 inning, pitching performance was not investigated in their study. To our knowledge, very few attempts have been made to quantify the changes in lower extremity function and pitching performance with increasing numbers of pitches in baseball pitchers. It is possible that lower extremity muscle fatigue diminishes energy transfer from the lower extremity to the trunk during baseball pitching, resulting in decreased ball velocity. Moreover, a fatigued lower extremity may adversely affect pitching accuracy.

The purpose of this study was to evaluate the effect of fatigue on lower extremity function and pitching performance in a simulated baseball game and to assess the correlation between lower extremity function and pitching performance. These data would be useful for constructing training, conditioning, and rehabilitation programs for baseball pitchers. Our hypothesis was that baseball pitchers would show significantly decreased lower extremity function and pitching performance in the game and that significant correlations would be found between lower extremity function and pitching performance.

MATERIALS AND METHODS

Hip abduction and adduction strength

Isometric muscle strength of hip abduction and adduction was measured using a dynamometer (T.K.K.3367b, Takei Scientific Instruments Co., Ltd., Niigata, Japan) with the participant in a seated position before and after the simulated game. The dynamometer was placed between the thighs. Then, fixation belts of the dynamometer were firmly worn around the distal end of each thigh (Fig. 1). The participant was instructed to maximally perform 5-sec isometric hip adduction by pushing the pads of the dynamometer or abduction by pulling the fixation belts of the dynamometer. The calibration of the dynamometer was always performed prior to each trial. The participant performed two trials in the measurements of hip abduction or adduction strength. The maximum value of the two trials was used for analysis. The participants were always given verbal encouragement during force generation.

Fig. 1

Positioning for the measurement of isometric hip abduction and adduction strength.

Squat jump

The height, mean/peak power, and mean/peak velocity for squat jump without arm swing were measured using a digital optical encoder (Gymaware, Kinetic Performance Technology, Canberra, Australia) before and after the simulated game. The optical encoder was positioned on the ground perpendicular to the movement of the body. The connection cable coupled to the encoder was attached via a tether to the belt of the participant; jump height was set to 0 m at upright standing position. Then, the participants performed the squat jump with their knee flexed at 90°, with their hands on the hips, and with the stance at hip width (Fig. 2). The examiners checked the knee angle with a goniometer before the jump and no reaction movement at the start of the jump. Participants were asked to hold the squat position for 3 sec before performing a maximal vertical jump. Additionally, they were instructed to jump as high and fast as possible. Data (jumping height, mean/peak power, and mean/peak velocity) regarding the maximal jump height of 2 trials was used for subsequent analysis.

Fig. 2

Positioning for squat jump without arm swing. Frontal (A) and lateral (B) views.

RESULTS

Pitching performance

Fig. 3 shows the changes of ball velocity from the 1st to 9th inning. Ball velocity significantly decreased in the 7th (128.4±5.7 km/hr, P=0.026, d=0.32) and 9th (127.8±6.8 km/hr, P=0.001, d=0.38) innings compared to the 1st inning (130.3±6.2 km/hr). On the other hand, pitching accuracy did not show significant change from the 1st inning (1st inning, 53.1%±21.1%; 2nd inning, 46.9%±24.3%; 3rd inning, 48.1%±18.7%; 4th inning, 45.1%±16.4%; 5th inning, 48.8%±23.8%; 6th inning, 43.2%± 18.2%; 7th inning, 45.7%±17.8%; 8th inning, 56.2%±21.4%; 9th inning, 44.4%±17.0%).

Fig. 3

Changes of ball velocity from the 1st to 9th inning (mean±standard deviation).

Hip muscle strength and squat jump

Table 1 displays the values of hip muscle strength and squat jump. Hip abduction (P=0.009, d=0.41) and adduction (P=0.001, d=0.47) strength significantly decreased after the simulated game. On the other hand, the height, mean/peak power, and mean/peak velocity for squat jump without arm swing showed no significant changes before and after the simulated game.

Table 1

Data regarding hip muscle strength and squat jump before and after a simulated game

Correlations between lower extremity function and pitching performance

The simulated game resulted in significantly decreased hip abduction and adduction strength and ball velocity. A significant correlation was found between decreased ball velocity in the 9th inning and decreased hip adduction strength immediately after the game (P=0.011, r=0.583) (Fig. 4).

Fig. 4

Correlation of the rate of change in ball velocity in the 9th inning with hip adduction strength after the simulated game.

DISCUSSION

In the present study, hip abduction and adduction strength significantly decreased after the simulated game. These findings would be attributed to muscle fatigue resulting from repetitive throwing motions. In baseball pitching, stride length is an important biomechanical parameter for generating greater translational energy using the downward slope of the pitching mound (Dillman et al., 1993; Fortenbaugh et al., 2009; Fry et al., 2017; Milewski et al., 2012). Hip abduction strength in the pivot leg helps stabilize the pelvis and lengthen the stride by preventing downward tilt of the contralateral pelvis during the wind-up and early cocking phases of baseball pitching (Kageyama et al., 2014; Laudner et al., 2010). After stride foot contact, the stride leg generates a braking force to decelerate the motions of the lower extremities and serves as an anchor in transforming the forward and vertical momentum into rotational components (MacWilliams et al., 1998). Kageyama et al. (2014) demonstrated that hip adduction torque on the stride leg at stride foot contact was significantly greater in high-ball-velocity pitchers than in low-ball-velocity pitchers, and suggested that the greater hip adduction torque contributes to the control/stabilization of the stride leg to increase the rotation and forward motion of the trunk after the late cocking phase of baseball pitching as well as the production of greater ground-reaction force on the stride leg, resulting in the generation of high ball velocity. Similarly, the hip abductors in the stride leg also possibly contribute to the control/stabilization of the stride leg after stride foot contact (Guido and Werner, 2012; Kageyama et al., 2014; MacWilliams et al., 1998; Milewski et al., 2012). Taken together, hip abductors and adductors are thought to play important roles in the gain of appropriate stride length as well as the smooth energy transfer from the stride leg to the trunk (as a part of the entire kinetic chain) during pitching. Our findings suggest that hip adduction strength is an important physical fitness factor for baseball pitchers to maintain the ball velocity during a game. On the other hand, although Mullaney et al. (2005) found minimal muscle fatigue in the hip musculature after pitching 7±2 inning (99±29 pitches per game), the change was not significant. Therefore, further accumulation of data is needed to clarify the effect of repetitive throwing motions on hip muscle strength in baseball pitchers.

Contrary to our expectation, in the present study all variables of the squat jump did not show significant decreases after the simulated game. Previous studies (Kageyama et al., 2014; MacWilliams et al., 1998) indicated that ball velocity correlates highly with the maximal push-off force (greater momentum by hip and knee extension) of the pivot leg generated during pitching, which supplies the initial forward momentum of the entire body in the direction of the pitch. Lehman et al. (2013) revealed that high ball velocity significantly correlated with the test score in a unilateral side jump in the frontal plane, which mimics the stride action of baseball pitching. Moreover, Murray et al. (2001) suggested that lower extremity muscle fatigue caused significant decreases in knee angle at ball release and ball velocity at the last inning of a simulated game in professional baseball pitchers. Taken together, extension power (force) of the lower extremities is thought to be a physical fitness factor that is related to ball velocity in baseball pitchers. However, the effect of repetitive throwing motions on jump performance was not found in the present study.

The present study has a few limitations. First, the lack of remarkable change in the present study may partly be attributed to limitations due to pitching in a simulated game (a noncompetitive environment) because a simulated game cannot completely replicate the conditions experimented during a competitive game (Escamilla et al., 2007). It is possible that baseball pitchers feel more physical and/or mental fatigue in an actual game than a simulated game, resulting in more decreased muscle function and pitching performance. Second, we measured hip muscle strength and jump performance only before and after the simulated game because we thought that the number of measurements should be limited to properly assess acute physical responses (fatigue) immediately after pitching. To date, very few studies have attempted to investigate the effects of repetitive throwing motions on lower extremity function in baseball pitchers. Thus, further research is required to clarify changes in various lower extremity functions with increasing numbers of pitches in baseball pitchers at various competitive levels. In particular, physically immature baseball pitchers may be susceptible to lower extremity muscle fatigue with increasing numbers of pitches (Erickson et al., 2016). Additionally, it was revealed that lower extremity power (vertical jump height and power) decreases with age in professional baseball pitchers (Mangine et al., 2013). Third, although we did not measure upper extremity and trunk functions in this study, it is possible that muscle fatigue of the upper extremity and/or trunk muscles was related to decreased ball velocity at the end of the simulated game.

In conclusion, our data showed that hip abductors and adductors of baseball pitchers are susceptible to muscle fatigue due to repetitive throwing motions. In addition, hip adduction strength is thought to be an important physical fitness factor for maintaining ball velocity during a game in baseball pitchers.

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