Age- and sex-dependence of muscle quality: Influence of intramuscular non-contractile tissues

This is the final version. Available on open access from Elsevier via the DOI in this recordPurpose Muscle quality is explained by the ratio between muscle size and strength. Conventionally, muscle size is evaluated without considering the composition of contractile and non-contractile tissues in muscle, hence the influence of non-contractile tissues on muscle quality is not fully understood, especially within aging muscle. This study investigated the differences in intramuscular non-contractile tissues between different age and sex groups, and investigated their influence on muscle quality. Methods Eighty-two older and 64 young females and males participated. Muscle cross-sectional area (quadriceps and hamstrings), separating contractile and non-contractile areas, was calculated from the magnetic resonance image of the right mid-thigh. Maximal voluntary isometric knee extension and flexion torque was measured. Torque/muscle area and torque/contractile area were calculated for each age and sex group. Results Non-contractile/muscle area was higher in older than in young individuals in both muscle groups (p females) (p < 0.05). Conclusions The results indicate that 1) the presence of non-contractile tissues varies by age and muscle groups, 2) the extensive presence of non-contractile tissues can contribute to the underestimation of its muscle quality, and 3) the sex differences in muscle quality are influenced by factors other than muscle composition

Neuromuscular Factors Related to Hamstring Muscle Function, Performance and Injury

Hamstring function is influenced by a number of neural, architectural and morphological factors, and the adaptability of these characteristics has important implications for optimizing performance and reducing injury risk. High rates of maximal or near-maximal hamstring force development are required to generate peak horizontal velocities during running, and this is largely determined by the extent to which these muscles can be voluntarily activated. Greater eccentric hamstring strength also correlates with better acceleration capacity and likely improves the ability to decelerate the lower limb during the presumably injurious terminal swing phase of high-speed running. The intra- and intermuscular coordination of the hamstrings appears to influence both hamstring muscle fatiguability and the risk of muscle strain injury. Muscle volume and architectural features such as fascicle length and pennation angle also influence hamstring function, and these vary considerably between hamstring muscles, between individuals and with training status. The adaptability of these features has been explored to a significant extent in recent times, and careful exercise selection allows selective targeting of individual hamstring muscles or muscle segments and this appears to influence the pattern of chronic adaptations such as muscle hypertrophy. Short fascicles within the often-injured long head of biceps femoris may predispose athletes to strain injury but these appear to respond in a contraction-mode-specific manner; lengthening after eccentric training and shortening after concentric training of 4 or more weeks. Conventional training with eccentric and concentric phases in each repetition can also lengthen fascicles, possibly in an excursion (muscle length)-dependent manner. A large biceps femoris muscle to proximal aponeurosis width ratio has been proposed as a potential risk factor for hamstring strain injury, although this is only supported by biomechanical modelling at the time of writing. High levels of anterior pelvic tilt and lateral trunk flexion during sprint running may also predispose athletes to hamstring strain injury, although the quantity of evidence for this is small at the moment. At present, the optimal methods for altering coordination and running technique are not known

Anatomy of the Hamstrings

This chapter will provide the anatomical foundation for the content to come in later portions of this book. It will begin with an overview of the proximal insertion sites of the muscles that comprise the hamstring group. The proximal tendons and musculotendinous junctions (MTJs) of semimembranosus, semitendinosus and the long and short heads of biceps femoris long head will then be described, highlighting the differences in structure between each of the muscles. The distinct architectural characteristics of each muscle belly (e.g. size, fascicle orientation within and between muscles) will be outlined, followed by the structure of the distal tendons and MTJs. Finally, a summary is provided of the neurovascular supply of the hamstrings