Selectively breeding for high voluntary physical activity in female mice does not bestow inherent characteristics that resemble eccentric remodeling of the heart,but the mini-muscle phenotype does

Physical activity engagement results in a variety of positive health outcomes,including a reduction in cardiovascular disease risk partially due to eccentric remodeling of the heart.The purpose of this investigation was to determine if four replicate lines of High Runner mice that have been selectively bred for voluntary exercise on wheels have a cardiac phenotype that resembles the outcome of eccentric remodeling.Adult females(average age 55 days)from the 4 High Runner and 4 non-selected control lines were anaesthetized via vaporized isoflurane,then echocardiographic images were collected and analyzed for structural and functional differences.High Runner mice in general had lower ejection fractions compared to control mice lines(2-tailed p=0.0236)and tended to have thicker walls of the anterior portion of the left ventricle(p=0.065).However,a subset of the High Runner individuals,termed mini-muscle mice,had greater ejection fraction(p=0.0006),fractional shortening percentage(p<0.0001),and ventricular mass at dissection(p<0.0027 with body mass as a covariate)compared to non-mini muscle mice.Mice from replicate lines bred for high voluntary exercise did not all have inherent positive cardiac functional or structural characteristics,although a genetically unique subset of mini-muscle individuals did have greater functional cardiac characteristics,which in conjunction with their previously described peripheral aerobic enhancements(e.g.,increased capillarity)would partially account for their increased VO2max.

Downhill running impairs peripheral but not central neuromuscular indices in elbow flexor muscles

The purpose of this study was to examine the effects of a 1-h downhill running exercise on the elbow flexor muscles’neuromuscular functions.Seventeen adults(Control[CON]:n=9;Experimental[EXP]:n=8)completed this study.The CON rested for 30 min while the EXP performed the downhill running.Before,10 min,24 h,and 48 h after the interventions,dependent variables(knee extensor muscle soreness,elbow flexion and knee extension isometric strength,elbow flexion resting twitch and voluntary activation[VA],and the biceps surface electromyography[EMG]amplitude)were measured.Knee extensor muscle soreness was significantly greater in the EXP than the CON group following the intervention throughout the entire 48 h.This was accompanied by the greater decline in the knee extension strength in the EXP than the CON(mean±SD:-6.9±3.4%vs.1.0±3.2%,p=0.044).The elbow flexion strength,VA,and EMG amplitude were not affected by the exercise.However,the decline of the elbow flexion resting twitch was greater in the EXP than the CON(±19.6±6.3%vs.8.7±5.9%,p=0.003).Therefore,the downhill running impaired the remote elbow flexor muscles at a peripheral level.