The effects of postactivation potentiation on golf club head speed.

In golf, an increase in club head speed (CHS) has been shown to increase driving distance and is correlated with handicap. The purpose of this study was to investigate the effect of a postactivation potentiation (PAP) intervention on CHS. A FlightScope launch monitor was used to record CHS in 16 golfers (aged 20.1 ± 3.24 years, handicap 5.8 ± 2.26) during 2 testing sessions that were separated by 1 hour, using a counterbalanced design. The mean CHS of 3 swings was recorded with (experimental) and without (control) 3 preceding countermovement jumps (CMJs). An increase in CHS of 2.25 mph (effect size, 0.16; p < 0.05) 1 minute after the CMJ intervention was recorded. Therefore, acute enhancements in CHS are possible when performing a CMJ before a golf drive. This may have implications for training and on-course performance enhancement as a result of increased driving distance and possible reductions in handicap; this PAP intervention is practically viable.

Interactive effects of joint angle, contraction state and method on estimates of achilles tendon moment arms.

The muscle-tendon moment arm is an important input parameter for musculoskeletal models. Moment arms change as a function of joint angle and contraction state and depend on the method being employed. The overall purpose was to gain insights into the interactive effects of joint angle, contraction state and method on the Achilles tendon moment arm using the center of rotation (COR) and the tendon excursion method (TE). Achilles tendon moment arms were obtained at rest (TErest, CORrest) and during a maximum voluntary contraction (CORMVC) at four angles. We found strong correlations between TErest and CORMVC for all angles (.72 ≤ r ≤ .93) with Achilles tendon moment arms using CORMVC being 33-36% greater than those obtained from TErest. The relationship between Achilles tendon moment arms and angle was similar across both methods and both levels of muscular contraction. Finally, Achilles tendon moment arms for CORMVC were 1-8% greater than for COR(rest).

Shoulder Pain, Function, and Ultrasound-Determined Structure in Elite Wheelchair-Using Para Athletes: An Observational Study.

PURPOSE: This study aimed to determine the relationship between shoulder pain, physical examination, and tissue pathology in manual wheelchair users competing in elite sport. METHODS: Eighty elite para athletes who used a manual wheelchair for daily mobility were recruited from international track (n = 40), field (n = 19), and powerlifting (n = 21) competitions. Athletes were surveyed regarding shoulder pain history and symptoms (Wheelchair User's Shoulder Pain Index (WUSPI)), whereas independent blind observers measured signs (Physical Examination of the Shoulder Scale (PESS)) and tissue pathology (Ultrasound Shoulder Pathology Rating Scale (USPRS)). Relationships between measures for the total cohort and for subgroups defined by sporting discipline were calculated. RESULTS: A large proportion of athletes reported a history of upper limb pain (39% dominant and 35% nondominant). For the total cohort, WUSPI score was 22.3 ± 26.9, PESS score was 7.4 ± 6.7, and USPRS score was 5.2 ± 4.0. There were no USPRS score differences between athlete subgroups; however, track athletes had lower WUSPI and PESS scores, especially compared with field athletes. The first principal component explained most of the variance in the WUSPI and PESS, which were strongly correlated (r = 0.71), and the second orthogonal component explained the USPRS, which did not correlate with either the PESS (r = 0.21) or WUSPI (r = 0.20). Subgroup analysis showed that track athletes had lower symptom scores for a given physical examination score. CONCLUSIONS: Elite para athletes who use manual wheelchairs for daily mobility have a high prevalence of shoulder symptoms, positive signs on physical examination, and ultrasound-determined tissue pathology. Ultrasound-determined tissue pathology does not correlate with symptoms or signs. This information can help to guide clinicians in managing shoulder problems in this athlete population at high risk of injury.

Development of a finite element musculoskeletal model with the ability to predict contractions of three-dimensional muscles.

Representation of realistic muscle geometries is needed for systematic biomechanical simulation of musculoskeletal systems. Most of the previous musculoskeletal models are based on multibody dynamics simulation with muscles simplified as one-dimensional (1D) line-segments without accounting for the large muscle attachment areas, spatial fibre alignment within muscles and contact and wrapping between muscles and surrounding tissues. In previous musculoskeletal models with three-dimensional (3D) muscles, contractions of muscles were among the inputs rather than calculated, which hampers the predictive capability of these models. To address these issues, a finite element musculoskeletal model with the ability to predict contractions of 3D muscles was developed. Muscles with realistic 3D geometry, spatial muscle fibre alignment and muscle-muscle and muscle-bone interactions were accounted for. Active contractile stresses of the 3D muscles were determined through an efficient optimization approach based on the measured kinematics of the lower extremity and ground force during gait. This model also provided stresses and strains of muscles and contact mechanics of the muscle-muscle and muscle-bone interactions. The total contact force of the knee predicted by the model corresponded well to the in vivo measurement. Contact and wrapping between muscles and surrounding tissues were evident, demonstrating the need to consider 3D contact models of muscles. This modelling framework serves as the methodological basis for developing musculoskeletal modelling systems in finite element method incorporating 3D deformable contact models of muscles, joints, ligaments and bones.

Tibialis anterior moment arm: effects of measurement errors and assumptions.

UNLABELLED: Accurate estimates of tibialis anterior (TA) muscle force are important in many contexts. Two approaches commonly used to estimate moment arms are the tendon excursion (TE) and geometric (GEO) methods. Previous studies report poor agreement between the two approaches. PURPOSE: The purposes of this study were to 1) assess the effect of methodological variations in the two methods of moment arm estimation and 2) determine how these variations affect agreement between the methods. METHODS: TA moment arms were determined using TE and GEO. Errors associated with tendon stretch/hysteresis, talus rotation relative to the foot, and the location of the line of action were investigated. RESULTS: For TE, large errors in moment arm estimates across the range of motion were found when tendon length changes (P = 0.001) were not corrected for. For GEO, the estimated moment arm was reduced at an ankle angle of -15° when discrepancies between talus and foot rotations were accounted for or when an alternative tendon line of action was used either separately (effect size (ES), 0.46 and 0.58, respectively; P > 0.05) or together (ES, 0.89; P > 0.05). TE-derived moment arms were smaller than GEO-derived moment arms (ES, 0.68-4.86, varying by angle) before accounting for sources of error. However, these differences decreased after error correction (ES, 0.09-1.20, P > 0.05). Nonetheless, the shape of the moment arm-joint angle relation was curvilinear for TE but linear for GEO. CONCLUSIONS: Of all methodological modifications, accounting for tendon length changes had the largest effect on TA moment arm estimates. We conclude that the TE method is viable to determine TA moment arms as long as changes in tendon length are accounted for.

Direct comparison of in vivo Achilles tendon moment arms obtained from ultrasound and MR scans.

Accurate and reliable estimation of muscle moment arms is a prerequisite for the development of musculoskeletal models. Numerous techniques are available to estimate the Achilles tendon moment arm in vivo. The purposes of this study were 1) to compare in vivo Achilles tendon moment arms obtained using the center of rotation (COR) and tendon excursion (TE) methods and 2) to assess the reliability of each method. For the COR method, magnetic resonance (MR) images from nine participants were obtained at ankle angles of -15°, 0°, and +15° and analyzed using Reuleaux' method. For the TE method, the movement of the gastrocnemius medialis-Achilles tendon junction was recorded using ultrasonography as the ankle was passively rotated through its range of motion. The Achilles tendon moment arm was obtained by differentiation of tendon displacement with respect to ankle angular excursion using seven different differentiation techniques. Moment arms obtained using the COR method were significantly greater than those obtained using the TE method (P < 0.01), but results from both methods were well correlated. The coefficient of determination between moment arms derived from the COR and TE methods was highest when tendon displacement was linearly differentiated over a ± 10° interval (R(2) = 0.94). The between-measurement coefficient of variation was 3.9% for the COR method and 4.5-9.7% for the TE method, depending on the differentiation technique. The high reliabilities and strong relationship between methods demonstrate that both methods are robust against their limitations. The large absolute between-method differences (∼ 25-30%) in moment arms have significant implications for their use in musculoskeletal models.