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Objectives: To compare muscle and bone health markers in adult males (aged 20-59 yrs) with and without muscular dystrophy (MD)., Methods: Participants included 11 Fascioscapulohumeral (FSH), 11 Becker's (Be), 9 limb girdle (LG), 11 Duchenne (DMD), and 14 non-dystrophic controls (CTRL). Physical activity was assessed using Bone (BPAQ) and disability specific (PASIPD) questionnaires. Bone QUS provided T- and Z scores from the Distal Radius (DR) and Mid-shaft tibia (MST). Tibialis anterior cross sectional area (TA ACSA ) was measured using B-mode ultrasound. Grip strength was measured in all but DMD., Results: Physical activity was lower in DMD, FSH and BeMD than CTRL (P<0.05), and lower in DMD than other MDs (P<0.01). T and Z scores were lower in DMD and Be than CTRL (DR, P<0.05); and lower in DMD than CTRL, LG, and FSH (MST, P<0.01). TA ACSA and grip strength was 35-59% and 50-58% smaller in MD than CTRL, respectively (P<0.01). Within MD, BPAQ correlated with bone QUS measures (r=0.42-0.38, P<0.01). PASIPD correlated with grip strength (r=0.65, P<0.01) and TA ACSA (r=0.46, P<0.01)., Conclusion: Muscle size, strength, and bone health was lower in adult males with MD compared to adult males without MD, the extent of this is partially determined by physical activity., Competing Interests: The authors have no conflict of interest.

Objectives: To describe muscle size and architecture of the gastrocnemius medialis (GM) muscle in eleven adult males with Duchenne Muscular Dystrophy (DMD, age 24.5±5.4 years), and a control group of eleven males without DMD (CTRL, age 22.1±0.9 years)., Methods: GM anatomical cross sectional area (ACSA), volume (VOL), physiological cross sectional area (PCSA), fascicle length (Lf) and pennation angle (θ) were assessed using B-Mode Ultrasonography. GM ACSA was measured at 25, 50 and 75% of muscle length (Lm), from which VOL was calculated. At 50% of Lm, sagittal plane images were analysed to determine GM Lf and θ. GM PCSA was calculated as: VOL/Lf. The ratio of Lf and Lm was also calculated., Results: GM ACSA at 50% Lm, VOL and PCSA were smaller in DMD males compared to CTRL males by 36, 47 and 43%, respectively (P<0.01). There were no differences in Lf and θ. GM Lm was 29% shorter in DMD compared to CTRL. Lf/Lm was 29% longer in DMD (P<0.01)., Conclusions: Unlike previous data in children with DMD, our results show significant atrophy in adult males with DMD, and no change in Lf or θ. The shorter Lm may have implications for joint flexibility., Competing Interests: The authors have no conflict of interest.

The aim of this investigation was to determine the effect of sustained monophasic oral contraceptive pill (MOCP) use on the in vivo passive stiffness of the gastrocnemius medialis (GM) muscle-tendon unit. Twenty four females volunteered for this study (age range 20-25 yrs); twelve participants had been taking the combined MOCP for a minimum of 12 months, and twelve participants, who had never taken the MOCP, formed a control group. Distal displacement of the GM myotendinous junction (MTJ) was measured during passive dorsiflexion at 2 Nm increments to 20 Nm, and at end range of motion using ultrasonography. In addition, GM MTJ displacement was measured at passive torques equivalent to 5, 10 and 15% of plantarflexion maximal voluntary contraction (MVC) torque, and relative to GM length. MOCP users had significantly greater GM MTJ displacement at all passive torques (P<0.01), reaching 40% more at 20 Nm; these displacements remained significantly different when MVC and GM length were accounted for (P<0.01). Passive muscle stiffness from 0-20 Nm was 31% less in MOCP users compared to non-users (P<0.01). In conclusion, based on the in vivo assessment of GM MTJ displacement, passive muscle stiffness is less in MOCP using females, compared to non-pill users.

The ability of a muscle to shorten and produce force is crucial for locomotion, posture, balance and respiration. During a contraction, myosin heads on the myosin filament propel the actin filament via ATP hydrolysis, resulting in shortening of the muscle and/or force generation. The maximal shortening velocity of a muscle fibre is largely determined by the myosin ATPase activity, while maximal force is primarily determined by the cross-sectional area. Since most muscles are pennate rather than parallel-fibred and work at different lever ratios, muscle architecture and joint-tendon anatomy has to be taken into account to obtain the force and velocity characteristics of a muscle. Additionally, the recruitment of agonistic and antagonistic muscles will contribute to the torque generated during a contraction. Finally, tendon compliance may impact on the rate of force rise and force generated if it is such that the muscle contraction proceeds in the ascending limb of the length-tension relation. Even when magnetic resonance imaging and ultrasound, combined with EMG and/or electrical stimulation, have been applied to relate changes in muscle contractile properties to alterations in muscle size and architecture during ageing and resistance training, a disproportionate change in muscle strength and size remains to be explained.

Neuropathic, metabolic, hormonal, nutritional and immunological factors contribute to the development of sarcopenia. This loss of muscle mass associated with ageing, is a main cause of muscle weakness, but the loss of muscle strength typically exceeds that of muscle size, with a resulting decrease in force per unit of muscle cross-sectional area. Recent evidence suggests that, in addition to a reduction in neural drive and in fibre specific tension, changes in muscle architecture contribute significantly to the loss of muscle force through alterations in muscle mechanical properties. Older muscle, however, maintains a high degree of plasticity in response to increased loading since considerable hypertrophy and a reversal of the alterations in muscle architecture associated with ageing are observed with resistive training.