Electrical and mechanical response of skeletal muscle to electrical stimulation after acute passive stretching in humans: a combined electromyographic and mechanomyographic approach

Two mechanisms have been suggested to explain stretching-induced maximum force depression: a mechanical alteration in the stretched muscle and an impairment of neural activation. Electrical stimulation allows standardization of the level of muscle activation without being limited by neural control. The aim of this study was to evaluate the stretching-induced changes in the electrical and mechanical properties of muscle during electrically elicited contractions. Twelve participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m; mean +/- standard error) underwent six electrical stimulations of the medial gastrocnemius muscle before and after stretching. During the contractions, surface electromyogram (EMG) and mechanomyogram (MMG) were recorded simultaneously together with force. After stretching we found: (i) no differences in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii) the peak force, the peak rate of force development, and the acceleration peak of force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively (P < 0.05). In conclusion, acute passive stretching did not change EMG properties but altered the mechanical characteristics of the contracting muscle. Indeed, muscle force-generating capacity and stiffness of the muscle-tendon unit were significantly impaired.     

Compression garments and cerebral blood flow: Influence on cognitive and exercise performance

This study aimed to describe the effect of compression garments on middle cerebral artery blood flow velocity (MCA_v) in relation to cognitive and exercise performance whilst cycling. In a randomised-controlled-cross-over design, 15 well-trained male cyclists were recruited to participate in three identical trials wearing loose fitting shorts (control), low-grade, or medium-grade compression garments. The protocol involved four 8?min increments of cycling at 30%, 50%, 70%, and 85% maximal power output and a 4?km time-trial. Participants undertook a cognitive Stroop task at baseline and at the midpoint of each increment. MCA_v was monitored with Transcranial Doppler Ultrasonography. Mean arterial pressure (MAP) and partial pressure of end-tidal CO₂ (P_etCO₂) were measured throughout. MCA_v, MAP, P_etCO₂, and reaction time of the complex Stroop task were influenced by exercise intensity, but not compression garments. Compression garments significantly affected cognitive accuracy in the complex Stroop task such that low-grade compression appeared to enhance cognitive accuracy in comparison to the control condition at the highest intensity (p?=?.010). Time-trial performance did not differ between the control (338.0?±?17.3 s), low-grade (338.7?±?18.7 s), or medium-grade (342.2?±?19.3 s) conditions (p?=?.114). Compression garments did not affect MCA_v during exercise or time-trial performance, but compression may be beneficial for improved cognitive accuracy during high-intensity exercise. Further research is required to elucidate the potential impact on cognitive performance.