John T. Jolly

The role of upper torso and pelvis rotation in driving performance during the golf swing

Abstract While the role of the upper torso and pelvis in driving performance is anecdotally appreciated by golf instructors, their actual biomechanical role is unclear. The aims of this study were to describe upper torso and pelvis rotation and velocity during the golf swing and determine their role in ball velocity. One hundred recreational golfers underwent a biomechanical golf swing analysis using their own driver. Upper torso and pelvic rotation and velocity, and torso-pelvic separation and velocity, were measured for each swing. Ball velocity was assessed with a golf launch monitor. Group differences (groups based on ball velocity) and moderate relationships (r ≥ 0.50; P < 0.001) were observed between an increase in ball velocity and the following variables: increased torso – pelvic separation at the top of the swing, maximum torso – pelvic separation, maximum upper torso rotation velocity, upper torso rotational velocity at lead arm parallel and last 40 ms before impact, maximum torso – pelvic separation velocity and torso – pelvic separation velocity at both lead arm parallel and at the last 40 ms before impact. Torso – pelvic separation contributes to greater upper torso rotation velocity and torso – pelvic separation velocity during the downswing, ultimately contributing to greater ball velocity. Golf instructors can consider increasing ball velocity by maximizing separation between the upper torso and pelvis at the top of and initiation of the downswing.

Pectoralis major tendon transfers above or underneath the conjoint tendon in subscapularis-deficient shoulders. An in vitro biomechanical analysis.

BACKGROUND Different operative techniques for transfer of the pectoralis major tendon have been proposed for the treatment of irreparable ruptures of the subscapularis tendon. The objective of this study was to compare the effects of two techniques of transferring the pectoralis major tendon (above or underneath the conjoint tendon) on glenohumeral kinematics during active abduction in a biomechanical model of a subscapularis-deficient shoulder. METHODS Six shoulder specimens were tested with a custom dynamic shoulder testing apparatus. After the kinematics of the intact shoulder were recorded, a complete tear of the subscapularis tendon was simulated surgically. A transfer of the clavicular portion of the pectoralis major muscle to the lesser tuberosity was then performed with the transferred tendon placed either above (tendon-transfer 1) or underneath (tendon-transfer 2) the conjoint tendon. For each condition, the maximum abduction angle as well as the external rotation angle and the superoinferior and anteroposterior humeral translations at the maximum abduction angle were recorded. RESULTS With the rotator cuff intact, the mean maximum glenohumeral abduction angle (and standard error of the mean) was 86.3 degrees +/- 2.1 degrees and the mean amount of external rotation at the maximum abduction angle was 5.5 degrees +/- 7.6 degrees . A complete tear of the subscapularis tendon decreased the mean maximum abduction angle to 40.8 degrees +/- 2.4 degrees (p < 0.001) and increased the mean external rotation to 91.8 degrees +/- 4.8 degrees (p < 0.001). The mean humeral translations in the anterior and superior directions (+3.4 +/- 0.5 and +6.3 +/- 0.3 mm, respectively) at the maximum abduction angle were also increased (p < 0.01 and p < 0.001) when compared with those in the intact shoulder. Significant differences were found in the mean maximum abduction angle as well as the mean external rotation angle and humeral translations (anterior and superior) at maximum abduction between the tendon-transfer-1 condition (63.2 degrees +/- 13.5 degrees , 82.4 degrees +/- 6.6 degrees , 4.0 +/- 1.8 mm, and 3.3 +/- 1.9 mm, respectively) and tendon-transfer-2 condition (89.5 degrees +/- 12.3 degrees , 45.7 degrees +/- 22.5 degrees , -0.6 +/- 2.0 mm, and 0.5 +/- 2.3 mm, respectively). The tendon-transfer-2 condition restored glenohumeral kinematics that were closer to those in the intact shoulder than were those resulting from the tendon-transfer-1 condition. CONCLUSIONS Transfer of the pectoralis major tendon in subscapularis-deficient shoulders partially restored the glenohumeral kinematics of the intact shoulder. One possible explanation for the superior effect of the tendon-transfer-2 condition is that, with a pectoralis major tendon transfer underneath the conjoint tendon, the line of action of the transferred tendon is closer to that of the subscapularis muscle.

RELATIONSHIP BETWEEN CYCLING MECHANICS AND CORE STABILITY

Core stability has received considerable attention with regards to functional training in sports. Core stability provides the foundation from which power is generated in cycling. No research has described the relationship between core stability and cycling mechanics of the lower extremity. The purpose of this study was to determine the relationship between cycling mechanics and core stability. Hip, knee, and ankle joint kinematic and pedal force data were collected on 15 competitive cyclists while cycling untethered on a high-speed treadmill. The exhaustive cycling protocol consisted of cycling at 25.8 km·h−1 while the grade was increased 1% every 3 minutes. A core fatigue workout was performed before the second treadmill test. Total frontal plane knee motion (test 1: 15.1 ± 6.0°; test 2: 23.3 ± 12.5°), sagittal plane knee motion (test 1: 69.9 ± 4.9°; test 2: 79.3 ± 10.1°), and sagittal plane ankle motion (test 1: 29.0 ± 8.5°; test 2: 43.0 ± 22.9°) increased after the core fatigue protocol. No significant differences were demonstrated for pedaling forces. Core fatigue resulted in altered cycling mechanics that might increase the risk of injury because the knee joint is potentially exposed to greater stress. Improved core stability and endurance could promote greater alignment of the lower extremity when riding for extended durations as the core is more resistant to fatigue.

The relationship between the orientation of the glenoid and tears of the rotator cuff

Our aim was to determine the most repeatable three-dimensional measurement of glenoid orientation and to compare it between shoulders with intact and torn rotator cuffs. Our null hypothesis was that glenoid orientation in the scapulae of shoulders with a full-thickness tear of the rotator cuff was the same as that in shoulders with an intact rotator cuff. We studied 24 shoulders in cadavers, 12 with an intact rotator cuff and 12 with a full-thickness tear. Two different observers used a three-dimensional digitising system to measure glenoid orientation in the scapular plane (ie glenoid inclination) using six different techniques. Glenoid version was also measured. The overall precision of the measurements revealed an error of less than 0.6 degrees. Intraobserver reliability (correlation coefficients of 0.990 and 0.984 for each observer) and interobserver reliability (correlation coefficient of 0.985) were highest for measurement of glenoid inclination based on the angle obtained from a line connecting the superior and inferior points of the glenoid and that connecting the most superior point of the glenoid and the most superior point on the body of the scapula. There were no differences in glenoid inclination (p = 0.34) or glenoid version (p = 0.12) in scapulae from shoulders with an intact rotator cuff and those with a full-thickness tear. Abnormal glenoid orientation was not present in shoulders with a torn rotator cuff.

The Effect of a Hill-Sachs Defect on Glenohumeral Translations, In Situ Capsular Forces, and Bony Contact Forces

Background: Hill-Sachs defects have been associated with failed repairs for anterior shoulder instability. However, the biomechanical consequences of these defects are not well understood because of the complicated interaction between the passive soft tissue and bony stabilizers. Hypothesis: The creation of a 25% Hill-Sachs defect would not significantly alter the glenohumeral translations but would increase the in situ forces in the glenohumeral capsule as well as the glenohumeral bony contact forces. Study Design: Controlled laboratory study. Methods: A robotic/universal force-moment sensor (UFS) testing system was used to apply joint compression (22 N) and an anterior or posterior load (44 N) to cadaveric shoulders (n = 9) with the skin and deltoid removed (intact) at 3 glenohumeral joint positions (abduction/external rotation): 0°/0°, 30°/30°, and 60°/60° (corresponds to 90°/90° of shoulder abduction/external rotation). A 25% bony defect on the posterolateral humeral head (defect) was then created in the most common position of anterior shoulder dislocation (90°/90°), and the loading protocol was repeated. A nonparametric repeated-measures Friedman test with a Wilcoxon signed-rank post hoc test was performed to compare translations, in situ forces in the capsule, and bony contact forces between each state (P < .05). Results:At 0°/0°, anterior translation significantly increased from 15.3 ± 8.2 mm to 16.6 ± 9.0 mm (P < .05) in response to an anterior load. At 30°/30°, anterior and posterior translations, respectively, significantly increased in response to both anterior (intact: 13.6 ± 7.1 mm vs defect: 14.2 ± 7 mm; P < .05) and posterior loads (intact: 15.7 ± 5.8 mm vs defect: 17.7 ± 5.1 mm; P < .05). In situ force in the capsule during anterior loading was increased in the defect state at both 60°/60° (intact: 38.9 ± 14.4 N vs defect: 43.2 ± 15.9 N; P < .05) and 30°/30° (intact: 39.6 ± 13.8 N vs defect: 45.6 ± 9.3 N; P < .05). The medial bony contact forces were also increased in the defect state at 30°/30° (intact: 25.0 ± 13.8 N vs defect: 28.9 ± 13.2 N; P < .05) during anterior loading. Conclusion: We believe that the stabilizing function of the intact capsule was the primary contributor to the finding of only small increases of anterior translation, capsule forces, and bony contact forces observed with a 25% Hill-Sachs defect in response to an anterior load. Clinical Relevance: These findings imply that a 25% Hill-Sachs defect in isolation may not be responsible for recurrent instability if the function of the capsule is restored to the intact state and that the presence of the Hill-Sachs defect may be a marker for significant concomitant injury to the anterior glenoid rim. However, the small changes in these parameters may have long-term implications for the development of osteoarthritis.

Does Repair of a Hill-Sachs Defect Increase Stability at the Glenohumeral Joint?

Background: The effect of osteoallograft repair of a Hill-Sachs lesion and the effect of allograft fit on glenohumeral translations in response to applied force are poorly understood. Purpose: To compare the impact of a 25% Hill-Sachs lesion, a perfect osteoallograft repair (PAR) of a 25% Hill-Sachs lesion, and an “imperfect” osteoallograft repair (IAR) of a 25% Hill-Sachs lesion on glenohumeral translations in response to a compressive load and either an anterior or posterior load in 3 clinically relevant arm positions. Study Design: Controlled laboratory study. Methods: A robotic/universal force-moment sensor testing system was used to apply joint compression (22 N) and an anterior or posterior load (44 N) to cadaveric shoulders (n = 9) with the skin and deltoid removed (intact) at 3 glenohumeral joint positions (abduction/external rotation): 0°/0°, 30°/30°, and 60°/60°. The 25% bony defect state, PAR state, and IAR state were created and the loading protocol was performed. Translational motion was measured in each position for each shoulder state. A nonparametric repeated-measures Friedman test with a Wilcoxon signed-rank post hoc test was performed to compare the biomechanical parameters (P < .05). Results: Compared with the defect shoulder, the PAR shoulder had significantly less anterior translation with an anterior load in the 0°/0° (15.3 ± 8.2 vs 16.6 ± 9.0 mm, P = .008) and 30°/30° (13.6 ± 7.1 vs 14.2 ± 7.0 mm, P = .021) positions. Compared with IAR, the PAR shoulder had significantly less anterior translation with an anterior load in the 0°/0° (15.3 ± 8.2 vs 16.6 ± 9.0 mm, P = .008) and 30°/30° (13.6 ± 7.1 vs 14.4 ± 7.1 mm, P = .011) positions, and the defect shoulder had significantly less anterior translation with an anterior load in the 30°/30° (14.2 ± 7.0 vs 14.4 ± 7.0 mm, P = .038) position. Conclusion: PAR resulted in the least translational motion at the glenohumeral joint. The defect shoulder had significantly less translational motion at the joint compared with the IAR. An IAR resulted in the most translational motion at the glenohumeral joint. This demonstrates the biomechanical importance of performing an osteoallograft repair in which the allograft closely matches the Hill-Sachs defect and fully restores the preinjury state of the humeral head. Clinical Relevance: This study demonstrates the importance of performing an osteoallograft repair of a Hill-Sachs defect that closely matches the preinjury state and restores normal humeral head anatomy.

Highly Proficient Golfers Exhibit Greater Consistency In Driving Ball Flight Characteristics Than Less Proficient Golfers: 2225

It is believed that consistency of golf ball flight characteristics (BFC) is more indicative of golf proficiency than traditional measures of golf performance such as club velocity (CV) and total driving distance (TD). Highly proficient golfers are believed to have more consistent BFC between swings than less proficient golfers. PURPOSE: To determine whether BFC consistency differs between highly proficient golfers and less proficient golfers. METHODS: Ninety male golfers (43.5 ± 14.4 years) performed ten golf swings with their own driver. A golf launch monitor was used to measure BFC. The mean and standard deviations (SD) of CV, ball velocity (BV), vertical launch angle (VLA), horizontal launch angle (HLA), backspin (BS), carry distance (CD), and TD were calculated for each subject using the five drives with the greatest TD. The SD of BV, CD, and TD were normalized (SDN) to their respective mean values. Lower SD and SDN were interpreted to represent greater consistency. Golfers were grouped based on proficiency by USGA handicap: low (L: <8, n=56), mid (M: 8-14.9, n=25), and high handicap (H: ≥15, n=9). One-way analysis of variance and Tukey’s post hoc procedure were used to determine differences between groups. Statistical significance was set a priori at p<0.05. RESULTS: There were no significant differences between groups for BS or CV consistency. Statistically significant differences are italicized in the table below.

Active Stability of the Glenohumeral Joint Decreases in the Apprehension Position

Muscle forces that compress the glenohumeral joint during midranges of motion may lead to increased translational forces in endrange positions, such as the apprehension position, where symptoms of anterior instability occur. The objective of this study was to quantify active stability provided by eight shoulder muscles in mid-range and end-range positions through muscle force vector analysis. Lines of action were derived from a standard geometric model and muscle force magnitudes were estimated with electromyography-based techniques. Resultant muscle force vectors were calculated by summing individual muscle force vectors. Compared to mid-range positions, lines of action of resultant force vectors were more anteriorly-directed in end-range positions. The deviation angle in the anterior direction was greatest (35°) and, consequently, stability was lowest in the apprehension position. Based on a sensitivity analysis, lines of action of resultant force vectors vary up to 6° within the population. In the apprehension position, muscle forces may promote anterior humeral head translation, predisposing the glenohumeral joint to anterior instability when other joint stabilizers are not functioning normally.Copyright