Sex differences in shoulder performance fatiguability are affected by arm position, dominance and muscle group.

BACKGROUND: Injury prevalence data, muscle strength, and fatiguability differ between males and females. In addition, arm spatial orientation affects muscle activation and strength of the shoulder muscles. Nevertheless, little research has been conducted in relation to the shoulder rotator muscles comparing men and women. Therefore, the main aim of of this study was to perform a comparative investigation between two arm spatial orientations (45° and 90° of abduction in the frontal plane) during a fatigue assessment of the internal rotator (IR) and external rotator (ER) shoulder muscles. Secondly, the interaction between sex and dominance with muscular performance was assessed. METHODS: Forty healthy sedentary participants, 20 males and 20 females took part in this study. Participants performed a fatigue resistance protocol consisting of 30 consecutive maximal concentric contractions of the IR and ER shoulder muscles in a supine position at a speed of 180°/s. The upper limb was abducted to an angle of 45° or 90° in the frontal plane and each participant was tested on the dominant and nom-dominant side, counterbalanced in order of administration. Performance measures of Induced Fatigue (IF; %), Cumulated Performance (C.Perf; J) and Best Repetition (BR; J) were calculated and used for analysis. IF represents the % difference between the amount of work done over the last 3 and first 3 repetitions, BR represents the largest amount of work done during a single contraction, and C.Perf represents the total amount of work done during all repetitions. RESULTS: Muscle group was the only factor to display significant variation when not considering other factors, with higher values for C.Perf (mean difference = 353.59 J, P < 0.0005), BR (mean difference = 14.21 J, P < 0.0005) and IF (mean difference = 3.65%, P = 0.0046). There was a significant difference between both angles, with higher values observed at 90° compared to 45° of abduction for C.Perf by ~ 7.5% (mean difference = 75 to 152 J) and ~ 10.8% (mean difference = 5.1 to 9.4 J) for BR in the ER, in males and females respectively (P < 0.0005). The dominant arm was significantly stronger than the non-dominant arm for C.Perf by 11.7% (mean difference = 111.58 J) for males and by 18% (mean difference = 82.77 J) for females in the ER at 45° abduction. At 90° abduction, only females were stronger in the dominant arm by 18.8% (mean difference = 88.17 J). Values for BR ranged from 9.2 to 21.8% depending on the abduction angle and sex of the athlete (mean difference = 2.44 - 4.85 J). Males were significantly stronger than females by 48.8 to 50.7% for values of C.Perf and BR in both the IR and ER (P < 0.0005). There was a significant difference between the ER and IR muscles, with significantly higher values observed for the IR in C.Perf (mean difference = 331.74 J) by 30.0% and in BR (mean difference = 13.31 J) by 26.64%. DISCUSSION: Differences in shoulder performance fatiguability between sexes are affected by arm position, arm dominance and muscle groups. In agreement with the literature, performance values in males were approximately 50% higher than in females. However, the amount of IF was no different between both sexes. Based on findings in literature, it could be suggested that this is due to differences between males and females in motor control and/or coordination strategies during repetitive tasks. In addition, we also observed the IR muscles to be significantly stronger than the ER muscles. It has long been established in literature that these observations are due to the muscle-size differences between both muscle groups, where the IR muscles can produce a larger amount of force due to the larger cross-sectional area. Results of our study found similar ER:IR ratios compared to previous reports. CONCLUSION: Therefore, these findings are useful for clinicians when monitoring rehabilitation programs in sedentary individuals following shoulder injuries.

Influence of a Field Hamstring Eccentric Training on Muscle Strength and Flexibility.

Muscle strength imbalances and poor flexibility are frequently described as risk factors for hamstring injury. Preventive strategies include eccentric exercises, but the influence of field eccentric exercises on these risk factors remains unclear. We investigated the influence of a field hamstring eccentric program on hamstring strength and flexibility. Twenty-seven amateur athletes were randomly assigned to an intervention (n=13) or control group (n=14). In the intervention group, participants were involved in 15 sessions of four eccentric exercises. Peak torque, hamstring-to-quadriceps ratios, passive and active flexibility were analyzed. No significant modifications of strength, passive or active flexibility were observed in the control group (p>0.05). Hamstring eccentric peak torque (+7.1%) and functional hamstring-to-quadriceps ratios (9.3%) were significantly increased (p<0.05) in the intervention group, but not concentric strength (p<0.05). Passive straight leg raise was significantly increased by 11.4° (+12.7%, p<0.001), but not active flexibility (+3.1%, p>0.05). In conclusion, a 6-week eccentric program, including four field exercises for hamstring muscles, is an effective method of improving eccentric strength, functional ratios and, especially, passive flexibility. As this program may be easily implemented in a real-world context, this association of multiple eccentric exercises might be useful in an injury prevention strategy.

Eccentric versus Concentric - Which Is the Most Stressful Cardiovascularly and Metabolically?

The purpose of this study was to compare the fatigability resistance profile and the physiological responses of strenuous concentric (CON) versus eccentric (ECC) isokinetic exercises. At two different sessions, 12 healthy sedentary male subjects (24.3 ± 2.5 years) performed strenuous CON and ECC isokinetic exercises. The protocol consisted of three sets of 12 maximal repetitions, separated by 30-s intervals, at a velocity of 60°·s for both flexor and extensor knee muscles of the dominant leg. Metabolic (ventilation, oxygen uptake, blood lactate concentration) and cardiovascular (HR, mean arterial blood pressure) parameters were registered before, throughout, and after the isokinetic session. The isokinetic data analysis revealed a more pronounced fatigue in the hamstrings than in the quadriceps in the ECC mode (fatigue index, ratio between the third and the first sets, of 94.8% ± 11.8% vs 86.4% ± 10.8%; P < 0.05). All physiological responses studied increased gradually during the isokinetic evaluation, both in CON and ECC modes. For total work normalized by physiological responses, cardiovascular and metabolic variables were lower in the CON than in the ECC mode, a sign of a weaker efficiency in CON mode (ratio between performance and physiological cost). In conclusion, the study shows a specific fatigability resistance profile consisting of an early decrease of ECC hamstring performance compared with the quadriceps profile. In addition, we confirm that physiological consequences are important during strenuous isokinetic exercises but ECC exercise produces less stress on the cardiovascular and the metabolic systems than does CON exercise.

Evolution of the trophy position along the tennis serve player's development.

The trophy position is a coaching cue for the tennis serve that usually corresponds to the racquet high point (RHP) during the preparatory action for the stroke. Mastering this position and its time of occurrence seems essential in overarm movements like in the tennis serve. Clinicians and coaches have a real interest in understanding the trophy position and its evolution during the development of the elite players at different ages. A 3D motion system was used to measure the kinematics of the serve. A group of high-level tennis players were selected for three different age groups: 8 adults (ITN 1), 8 teenagers (ITN 3) and 8 children (ITN 5-6). Results show a modified pattern sequence of the tennis serve between children and adult players. RHP appears earlier relative to impact for children (-0.54 ± 0.10 s) than for adults (-0.36 ± 0.11 s) and teenagers (-0.33 ± 0.05 s) (p = 0.007). At RHP, children present lower trunk transverse plane rotation (p < 0.003) and higher shoulder external rotation (p < 0.003). These positions for the child players may represent an increased risk of shoulder and trunk injury than for older players and contribute to a lower racquet resultant velocity at impact.

Inter-Session Reliability of the Tennis Serve and Influence of the Laboratory Context.

To meet the demand of a player's entourage (e.g., coaches and medical staff), it is important for the biomechanics specialist to perform repeatable measures. To the best of our knowledge, to date, it has not been demonstrated whether similar results are obtained between two sessions of testing or between laboratory and field sport kinematic protocols with regard to the tennis serve. This study had two primary aims. First, the inter-session repeatability of biomechanical variables of a tennis serve was evaluated. Second, the differences between laboratory and field evaluations were studied. Thirteen national tennis players (ITN 3) performed the same 28 markers' set laboratory test twice two weeks apart, and other thirteen national players (ITN 3) performed two 4 markers' set tests both in the laboratory and on an official tennis court one week apart. A 3D motion system was used to measure lower-limb, pelvis, trunk, dominant arm and racket kinematics. A force plate was used to evaluate kinetics of legs' drive in the laboratory. A personal method based on a point scoring system was developed to evaluate the ball landing location accuracy. We observed that the majority of the studied variables were acceptable for excellent relative reliability for the inter-session analysis. We also showed that the impact of the laboratory versus field context on the player's serve was limited.

Reliability of unipodal and bipodal counter movement jump landings in a recreational male population.

Movement patterns during landing have been suggested to be related to injury risk. The purpose of this study was to determine the inter-session reliability of kinematic variables and ground reaction forces during landing in a population of male recreational athletes after a counter movement jump. Both unipodal and bipodal landings were evaluated. Furthermore, the possibility to improve landing reliability with a verbal instruction was also studied. Twenty-four male volunteers with no history of lower extremity trauma were randomly assigned to two groups (with and without verbal landing instruction). An optoelectronic 3D system and force plates were used to measure the lower limb joint angles and the ground reaction forces during landing. Intraclass correlation values show moderate to excellent inter-session reliability for the bipodal task (ICC average: 0.80, range: 0.46-0.97) and poor to excellent reliability for the unipodal task (ICC average: >0.75, range: 0.20-0.95). However, large standard errors of measurement values at the ankle joint at impact (27.6 ± 11.5°) and for the vertical ground reaction forces (394 ± 1091 N) show that some variables may not be usable in practice. The verbal instruction had a negative effect on the reliability of unipodal landing but improved the reliability of bipodal landing. These findings show that the reliability of a landing task is influenced by its motor complexity as well as the instruction given to the subject.