Michelle Sabick

The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton. The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retro-torsion. Descriptive laboratory study. A total of 14 elite youth baseball pitchers (mean age, 12.1 +/- 0.4 years) were filmed from the front and dominant side while throwing fastballs in a simulated game. The net force and torque acting on the humerus throughout the throwing motion were calculated using standard biomechanical techniques. The external rotation torque about the long axis of the humerus reached a peak value of 17.7 +/- 3.5 N.m (2.7% +/- 0.3% body weight x height) just before maximum shoulder external rotation. A sho...

Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion. The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations. Peak humeral axial torque reached a mean value of 92 +/- 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures. Fractures are most likely to occur near the time...

The purpose of this study was to determine the biomechanical and anthropometric factors contributing to elbow valgus torque during pitching. Video data of 14 youth pitchers throwing fastballs were used to calculate shoulder and elbow kinematics and kinetics. Peak elbow valgus torque averaged 18 Nm and occurred just before maximal shoulder external rotation. The magnitude of valgus torque was most closely correlated with the thrower's weight. When subject weight and height were controlled for, maximum shoulder abduction torque and maximum shoulder internal rotation torque were most strongly associated with elbow valgus torque, accounting for 85% of its variance (P <.001). When only kinematic variables were considered, maximum shoulder external rotation accounted for 33% of the variance in valgus torque. Given that the biomechanical variables correlated with peak valgus torque are not easily modifiable, limiting the number of innings pitched is likely the best way to reduce elb...

Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion. The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations. Peak humeral axial torque reached a mean value of 92 +/- 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures. Fractures are most likely to occur near the time of maximum shoulder external rotation when humeral torque peaks. Pitchers whose elbows were more extended at stride foot contact tended to have lower peak humeral torques.

Despite considerable advances in the understanding of glenohumeral (GH) biomechanics and glenoid labral pathologies, arthroscopy remains the only definitive means of SLAP lesion diagnosis. Unfortunately, natural GH anatomic variants limit the reliability of radiographic ...

The purpose of this study was to identify multijoint lower extremity kinematic and kinetic synergies in weightlifting and compare these synergies between joints and across different external loads. Subjects completed sets of the clean exercise at loads equal to 65, 75, and 85% of their estimated 1-RM. Functional data analysis was used to extract principal component functions (PCF's) for hip, knee, and ankle joint angles and moments of force during the pull phase of the clean at all loads. The PCF scores were then compared between joints and across loads to determine how much of each PCF was present at each joint and how it differed across loads. The analyses extracted two kinematic and four kinetic PCF's. The statistical comparisons indicated that all kinematic and two of the four kinetic PCF's did not differ across load, but scaled according to joint function. The PCF's captured a set of joint- and load-specific synergies that quantified biomechanical function of the lower extremity during Olympic weightlifting and revealed important technical characteristics that should be considered in sports training and future research.

The 'yips' is a psychoneuromuscular impediment affecting execution of the putting stroke in golf. Yips symptoms of jerks, tremors and freezing often occur during tournament golf and may cause performance problems. Yips-affected golfers add approximately 4.7 strokes to their scores for 18 holes of golf, and have more forearm electromyogram activity and higher competitive anxiety than nonaffected golfers in both high and low anxiety putting conditions. The aetiology of the yips is not clear. To determine whether the yips is a neurological problem exacerbated by anxiety, or whether the behaviour is initiated by anxiety and results in a permanent neuromuscular impediment. In phase I, golf professionals assisted investigators in developing a yips questionnaire that was sent to tournament players (<12 handicap) to establish the prevalence and characteristics of the yips. Phase II measured putting behaviour in scenarios that contribute to the yips response. Four self-reported yips and 3 nonaffected golfers putted 3 scenarios using an uncorrected grip and a standard length putter. Heart rate was superimposed on the videotape and the putter grip was instrumented with strain gauges to measure grip force. Electromyograms and relative putting performance were also measured. The questionnaire was sent to 2,630 tournament players, of whom 1,031 (39%) responded (986 men and 45 women). Of these, 541 (52%) perceived they experienced the yips compared with 490 (48%) who did not. Yips-affected golfers reported that the most troublesome putts were 3, 4 and 2 feet (0.9, 1.2 and 0.6 metres) from the hole. Fast, downhill, left-to-right breaking putts and tournament play also elicited the yips response. Golfers affected by the yips had a faster mean heart rate, increased electromyogram activity patterns and exerted more grip force than nonrffected golfers and had a poorer putting performance. For <10 handicap male golfers and <12 handicap female golfers, the prevalence of the yips is between 32.5% and 47.7%, a high proportion of serious golfers. This high prevalence suggests that medical practitioners need to understand the aetiology of the yips phenomenon so that interventions can be identified and tested for effectiveness in alleviating symptoms. Although previous investigators concluded that the yips is a neuromuscular impediment aggravated but not caused by anxiety, we believe the yips represents a continuum on which 'choking' (anxiety-related) and dystonia symptoms anchor the extremes. The aetiology may well be an interaction of psychoneuromuscular influences. Future research to test the effect of medications such as beta-blockers should assist in better identifying the contributions these factors make to the yips phenomenon.