The effects of accumulated muscle fatigue on the mechanomyographic waveform: implications for injury prediction.

PURPOSE: Muscle fatigue has been identified as a risk factor for spontaneous muscle injuries in sport. However, few studies have investigated the accumulated effects of muscle fatigue on human muscle contractile properties. This study aimed to determine whether repeated bouts of exercise inducing acute fatigue leads to longer-term fatigue-related changes in muscle contractile properties. METHODS: Maximum voluntary contraction (MVC), electromyographic (EMG) and mechanomyographic (MMG) measures were recorded in the biceps brachii of 11 participants for 13 days, before and after a maximally fatiguing exercise protocol. The exercise protocol involved participants repetitively lifting a weight (concentric contractions only) equal to 40 % MVC, until failure. RESULTS: A significant (p < 0.05) acute pre- to post-exercise decline of biceps brachii MVC and median power frequency (MPF) was observed each day, whilst no difference existed between pre-exercise MVC or MPF values on subsequent days (days 2-13). However, decreases in number of lift repetitions and in pre-exercise MMG values of muscle belly displacement, contraction velocity and half-relaxation velocity were observed through to day 13. CONCLUSIONS: Whilst MVC and MPF measures resolved by the following day's test session, MMG measures indicated an ongoing decrement in muscle performance through days 2-13 consistent with the decline in lift repetitions observed. These results suggest that MMG may be more sensitive in detecting accumulated muscle fatigue than the 'gold standard' measures of MVC/MPF. Considering that muscle fatigue leads to injury, the on-going monitoring of MMG derived contractile properties of muscles in athletes may aid in the prediction of fatigued-induced muscle injury.

Anatomy of the long head of biceps femoris: An ultrasound study.

Hamstring strains, particularly involving the long head of biceps femoris (BFlh) at the proximal musculotendinous junction (MTJ), are commonly experienced by athletes. With the use of diagnostic ultrasound increasing, an in-depth knowledge of normal ultrasonographic anatomy is fundamental to better understanding hamstring strain. The aim of this study was to describe the architecture of BFlh, using ultrasonography, in young men and cadaver specimens. BFlh morphology was examined in 19 healthy male participants (mean age 21.6 years) using ultrasound. Muscle, tendon and MTJ lengths were recorded and architectural parameters assessed at four standardised points along the muscle. Measurement accuracy was validated by ultrasound and dissection of BFlh in six male cadaver lower limbs (mean age 76 years). Intra-rater reliability of architectural parameters was examined for repeat scans, image analysis and dissection measurements. Distally the BFlh muscle had significantly (P < 0.05) shorter fascicles and larger pennation angles than proximal sites. Agreement between ultrasound and dissection (cadaver study) was excellent for all architectural parameters, except pennation angle (PA), and MTJ length. All other measures demonstrated good-excellent repeatability. BFlh is not uniform in architecture when imaged using ultrasound. It is likely that its distal-most segment is better suited for force production in comparison to the more proximal segments, which show excursive potential, traits which possibly contribute to the high rate of injury at the proximal MTJ. The data presented in this study provide specific knowledge of the normal ultrasonographic anatomy of BFlh, which should be of assistance in analysing BFlh injury via imaging. Clin. Anat. 29:738-745, 2016. © 2016 Wiley Periodicals, Inc.