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Frank Nugent, Thomas Comyns, Alan Nevill and Giles D. Warrington

that large amounts of practice, typically around 11 to 20 hours per week, are required to develop efficient stroke mechanics. 2 , 3 , 7 In recent years, a number of studies have investigated the effects of a low-volume, high-intensity training (HIT) program versus a low-intensity, high-volume training

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Helen G. Hanstock, Andrew D. Govus, Thomas B. Stenqvist, Anna K. Melin, Øystein Sylta and Monica K. Torstveit

Trained endurance athletes often undertake a training-intensity distribution including large volumes (≥80%) of low-intensity training (LIT) with smaller volumes of moderate-intensity training near the lactate threshold (5–15%) and high-intensity training (HIT; <10%), typically distributed in a

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Kristina Amrani, Andrew Gallucci and Marshall Magnusen

Key Points ▸ Data-based interval hitting programs for collegiate-level tennis players have yet to be documented in the literature. ▸ Athletic trainers can utilize recorded data of sport volumes to generate programs. ▸ Developing individualized hitting programs benefits all members of the

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Rafael F. Escamilla, Glenn S. Fleisig, Coop DeRenne, Marcus K. Taylor, Claude T. Moorman III, Rodney Imamura, Edward Barakatt and James R. Andrews

We propose that learning proper hitting kinematics should be encouraged at a young age during youth baseball because this may help reinforce proper hitting kinematics as a player progresses to higher levels of baseball in their adult years. To enhance our understanding between youth and adult baseball hitting, kinematic and temporal analyses of baseball hitting were evaluated with a high-speed motion analysis system between 12 skilled youth and 12 skilled adult baseball players. There were only a small number of temporal differences between youth and adult hitters, with adult hitters taking significantly greater time than youth hitters during the stride phase and during the swing. Compared with youth hitters, adult hitters a) had significantly greater (p < .01) lead knee flexion when the hands started to move forward; b) flexed the lead knee over a greater range of motion during the transition phase (31° versus 13°); c) extended the lead knee over a greater range of motion during the bat acceleration phase (59° versus 32°); d) maintained a more open pelvis position at lead foot off ground; and e) maintained a more open upper torso position when the hands started to move forward and a more closed upper torso position at bat-ball contact. Moreover, adult hitters had greater peak upper torso angular velocity (857°/s versus 717°/s), peak left elbow extension angular velocity (752°/s versus 598°/s), peak left knee extension angular velocity (386°/s versus 303°/s), and bat linear velocity at bat-ball contact (30 m/s versus 25 m/s). The numerous differences in kinematic and temporal parameters between youth and adult hitters suggest that hitting mechanics are different between these two groups.

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Rafael F. Escamilla, Glenn S. Fleisig, Coop DeRenne, Marcus K. Taylor, Claude T. Moorman III, Rodney Imamura, Edward Barakatt and James R. Andrews

A motion system collected 120-Hz data from 14 baseball adult hitters using normal and choke-up bat grips. Six swings were digitized for each hitter, and temporal and kinematic parameters were calculated. Compared with a normal grip, the choke-up grip resulted in 1) less time during stride phase and swing; 2) the upper torso more opened at lead foot contact; 3) the pelvis more closed and less bat linear velocity at bat-ball contact; 4) less range of motion of the upper torso and pelvis during swing; 5) greater elbow flexion at lead foot contact; and 6) greater peak right elbow extension angular velocity. The decreased time during the stride phase when using a choke-up grip implies that hitters quicken their stride when they choke up. Less swing time duration and less upper torso and pelvis rotation range of motion using the choke-up grip supports the belief of many coaches and players that using a choke-up grip results in a “quicker” swing. However, the belief that using a choke-up grip leads to a faster moving bat was not supported by the results of this study.

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Takatoshi Higuchi, Jun Morohoshi, Tomoyuki Nagami, Hiroki Nakata and Kazuyuki Kanosue

The effectiveness of fastballs of equivalent speed can differ; for example, one element of this difference could be due to the effect of rate and orientation of ball spin on launched ball trajectory. In the present experiment, baseball batters’ accuracy in hitting fastballs with different backspin rates at a constant ball velocity of 36 m/s was examined. Thirteen skilled baseball players (professionals, semiprofessionals, and college varsity players) participated in the study. The movements of bat and ball were recorded using two synchronized high-speed video cameras. The Pearson product-moment correlation coefficient (r) was calculated and used to analyze the relationship between ball backspin rate and the vertical distance between ball center and sweet spot at the moment of ball-bat impact. Ball backspin rate was positively correlated with increases in the distance from the optimal contact point of the swung bat (sweet spot) to the actual point of contact (r = .38, P < .001). Batters were most effective at the usual backspin rate for the ball velocity used. The decrease in accuracy of the batter’s swing that was observed when the fastball’s backspin deviated from the usual rate likely occurred because experienced batters predict ball trajectory from perceived ball speed.

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Yoichi Iino, Atsushi Fukushima and Takeji Kojima

The purpose of this study was to investigate the relevance of hip joint angles to the production of the pelvic rotation torque in fast-pitch softball hitting and to examine the effect of ball height on this production. Thirteen advanced female softball players hit stationary balls at three different heights: high, middle, and low. The pelvic rotation torque, defined as the torque acting on the pelvis through the hip joints about the pelvic superior–inferior axis, was determined from the kinematic and force plate data using inverse dynamics. Irrespective of the ball heights, the rear hip extension, rear hip external rotation, front hip adduction, and front hip flexion torques contributed to the production of pelvic rotation torque. Although the contributions of the adduction and external rotation torques at each hip joint were significantly different among the ball heights, the contributions of the front and rear hip joint torques were similar among the three ball heights owing to cancelation of the two torque components. The timings of the peaks of the hip joint torque components were significantly different, suggesting that softball hitters may need to adjust the timings of the torque exertions fairly precisely to rotate the upper body effectively.

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Edwin Van Thiel and Bert Steenbergen

In this study, we examined the degree and timing of shoulder displacements during hitting, reaching, and grasping movements performed by young adults with hemiparetic cerebral palsy. The participants performed unimanual and bimanual arm movements towards targets and objects of different sizes. On the basis of the assumption that shoulder displacement due to trunk translation and rotation is a successful, adaptive reaction to reduced joint mobility in the affected arm, the fluency of hand displacements was expected to remain invariant under variations of shoulder displacement as is also the case in healthy participants. The results point in this direction. With respect to the timing of shoulder displacement, prior research suggested that hemiparetic movements can be characterized by inconsistent motion-timing patterns—that is, the timing of shoulder and hand-displacement onsets varied between trials. Therefore, the within-subject variability of the movement-onset asynchrony between hand and ipsilateral shoulder displacement was expected to be larger on the impaired side than on the unimpaired side. This prediction was not confirmed. which challenges these earlier conclusions. Additionally. we also examined the peak-velocity asynchrony of the hand and shoulder. Contrary to the onset asynchrony, the peak asynchrony varied between the hitting and reaching task and between the hitting and grasping task. For the reaching and grasping tasks, there were also significant differences between hands. Again, variability of the (peak-velocity) asynchrony was not significantly increased when comparing the impaired hand with the unimpaired hand. The results suggests that the hemiparetic participants were capable of flexibly recruiting and sequencing the various degrees of freedom of their impaired side required for successful task completion, albeit in different magnitudes and sequenced differently.

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David Whiteside, Olivia Cant, Molly Connolly and Machar Reid

Context:

Quantifying external workload is fundamental to training prescription in sport. In tennis, global positioning data are imprecise and fail to capture hitting loads. The current gold standard (manual notation) is time intensive and often not possible given players’ heavy travel schedules.

Purpose:

To develop an automated stroke-classification system to help quantify hitting load in tennis.

Methods:

Nineteen athletes wore an inertial measurement unit (IMU) on their wrist during 66 video-recorded training sessions. Video footage was manually notated such that known shot type (serve, rally forehand, slice forehand, forehand volley, rally backhand, slice backhand, backhand volley, smash, or false positive) was associated with the corresponding IMU data for 28,582 shots. Six types of machine-learning models were then constructed to classify true shot type from the IMU signals.

Results:

Across 10-fold cross-validation, a cubic-kernel support vector machine classified binned shots (overhead, forehand, or backhand) with an accuracy of 97.4%. A second cubic-kernel support vector machine achieved 93.2% accuracy when classifying all 9 shot types.

Conclusions:

With a view to monitoring external load, the combination of miniature inertial sensors and machine learning offers a practical and automated method of quantifying shot counts and discriminating shot types in elite tennis players.

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