Sensor Location Matters When Estimating Player Workload for Baseball Pitching.

Estimating external workload in baseball pitchers is important for training and rehabilitation. Since current methods of estimating workload through pitch counts and rest days have only been marginally successful, clubs are looking for more sophisticated methods to quantify the mechanical loads experienced by pitchers. Among these are the use of wearable systems. While wearables offer a promising solution, there remains a lack of standards or guidelines for how best to employ these devices. As a result, sensor location and workload calculation methods vary from system to system. This can influence workload estimates and blur their interpretation and utility when making decisions about training or returning to sport. The primary purpose of this study was to determine the extent to which sensor location influences workload estimate. A secondary purpose was to compare estimates using different workload calculations. Acceleration data from three sensor locations-trunk, throwing upper arm, and throwing forearm-were collected from ten collegiate pitchers as they threw a series of pitches during a single bullpen session. The effect of sensor location and pitch type was assessed in relation to four different workload estimates. Sensor location significantly influenced workload estimates. Workload estimates calculated from the forearm sensor were significantly different across pitch types. Whole-body workload measured from a trunk-mounted sensor may not adequately reflect the mechanical loads experienced at throwing arm segments. A sensor on the forearm was the most sensitive to differences in workloads across pitch types, regardless of the calculation method.

Now you see, now you don't the influence of visual occlusion on racket and ball kinematics in the tennis serve.

The serve is considered amongst the most important strokes in tennis. Not surprisingly, the development of a mechanically consistent and proficient serve is paramount. Correspondingly, drills that involve players serving with their eyes closed are thought to promote mechanical consistency. The purpose of this study was therefore to contrast the effect of the removal of visual feedback on ball and racket kinematics in the serve. A 10-camera 500-Hz VICON MX motion analysis system recorded the service actions of eight elite young players as they performed three serves with eyes open and three serves with eyes closed. Removal of vision resulted in considerable differences in both racket and ball kinematics, with players failing to make contact on 16 of 24 serves. Temporally, the preparation phase was significantly shorter with eyes closed. Spatially, the ball was located 6.5 cm further to the right at zenith, and 13 cm higher at impact with eyes closed. These results highlight that the serve is not entirely pre-programmable, and that visual feedback is critical to the spatiotemporal regulation of the serve. In turn, coaches need to be aware of the implications of modifying visual feedback in serve, and ensure that the consequence is congruent with their intent.

Does perceptual or motor experience influence the perception of global and joint-specific kinematic changes in complex movement patterns?

The perception and identification of technical errors during skill execution is a critical component in coaching, because it provides the foundation for skill analysis, instruction, and feedback provision. In this study, we examined the influences of perceptual and motor experience on the perception of kinematic change in a technical evaluation task that is common in coaching. A total of 21 expert coaches, stratified by playing ("motor") expertise, as well as ten novice coaches and ten current players, observed video and point-light displays of a service action and recorded written judgments on whether the serve had changed from one video clip to the next. Three kinematic variables were manipulated: maximum knee flexion, maximum trunk rotation, and ball toss position at zenith. Coaching experience provided no additional benefit when perceiving global (holistic) changes in the service action, and limited if any benefit when perceiving specific changes in the observed kinematics. A significant expertise effect showed that expert coaches have increased sensitivity when detecting smaller changes in knee flexion. Changes in trunk rotation appeared difficult to perceive for all groups, whereas changes in lateral ball toss position were easily perceived. Motor experience did not influence the perception of global kinematics and provided no benefit above perceptual experience alone when perceiving specific kinematic changes. Collectively, the findings demonstrate that experienced coaches have the capacity to detect relatively small changes in kinematics; however, the ability to detect changes does not appear to be influenced by the extent of their own expertise in producing the movement pattern being evaluated.

Another day, another tennis coaching intervention, but does this one do what coaches purport?

A proficient serve is critical to successful tennis performance, and consequently coaches and players devote considerable time refining this stroke. In so doing, a wide variety of interventions are used or trialled, generally with very little empirical support. This study examined the efficacy of a commonly used service intervention, where players focus on exaggerating their finish (arabesque) position to promote specific changes in lower limb and trunk kinematics. The kinematics of eight high-performance junior players hitting flat serves were compared to the acute changes in kinematics elicited by the arabesque follow through position on serves using a 10-camera VICON MX motion analysis system. The significantly greater front (landing leg) hip flexion (p < 0.05) and forward trunk flexion (p < 0.05) confirmed the more exaggerated arabesque landing position following the arabesque instruction. The arabesque instruction resulted in increased frontal plane trunk range of motion and peak angular velocity in the forward swing, and increased leg drive during the drive phase. Practically, the results support the use of the arabesque instruction, effectively promoting the desired acute changes in trunk kinematics (i.e. increased frontal plane trunk rotation angular velocity) and leg drive (i.e. increased back knee extension angular velocity and front/back vertical hip velocity).

Exploring the kinaesthetic sensitivity of skilled performers for implementing movement instructions.

The capability to effectively control or adapt a movement pattern based on instructional feedback is essential for effective motor skill learning in high-level sport, as it is in other domains such as rehabilitation or music. Despite this, little is known about the capabilities of skilled athletes to use kinematic feedback to purposefully modify complex movements. This study examined the accuracy with which skilled junior tennis players could translate specific kinematic feedback into appropriate modifications of their service actions. Participants were required to either increase or decrease maximum knee flexion or shift impact position laterally by incremental amounts. Further, participants were required to execute their serve with the smallest increase and decrease in these kinematic components as they could consciously produce. Inherent variability within the desired target parameters was calculated to add context to the athlete's accuracy. Results demonstrated that while participants had considerable control over their movements, only some instructions were executed with accuracy greater the variability normally present within their movement. As the required change in knee flexion and impact position increased, absolute accuracy of implementation decreased. These findings are discussed with reference to the smallest controllable changes produced by the athletes and the variability within their actions.

A kinematic comparison of the overhand throw and tennis serve in tennis players: how similar are they really?

Tennis coaches often use the fundamental throwing skill as a training tool to develop the service action. However, recent skill acquisition literature questions the efficacy of non-specific training drills for developing complex sporting movements. Thus, this study examined the mechanical analogy of the throw and the tennis serve at three different levels of development. A 500 Hz, 22-camera VICON MX motion capture system recorded 28 elite female tennis players (prepubescent (n = 10), pubescent (n = 10), adult (n = 8)) as they performed flat serves and overhand throws. Two-way ANOVAs with repeated measures and partial correlations (controlling for group) assessed the strength and nature of the mechanical associations between the tasks. Preparatory mechanics were similar between the two tasks, while during propulsion, peak trunk twist and elbow extension velocities were significantly higher in the throw, yet the peak shoulder internal rotation and wrist flexion angular velocities were significantly greater in the serve. Furthermore, all of these peak angular velocities occurred significantly earlier in the serve. Ultimately, although the throw may help to prime transverse trunk kinematics in the serve, mechanics in the two skills appear less similar than many coaches seem to believe. Practitioners should, therefore, be aware that the throw appears less useful for priming the specific arm kinematics and temporal phasing that typifies the tennis serve.