Handgrip Training with Chronic Concomitant Exposure to Moderate Altitude Improves Blood Pressure Responses and Delays the Onset of Fatigue

Abstract

Exposure to moderate altitude (~2500 m) elicits a sympathoexcitatory response. There may also be long term changes such as a reduction in muscular strength and a quicker onset of muscular fatigue. The purpose of this study was to determine whether a training program with concomitant hypoxic exposure could blunt cardiovascular and neural responses, as well as delay the onset of fatigue. Twelve healthy males had heart rate (HR) and blood pressure (systolic, SBP; diastolic, DBP) measured during baseline (BL), static handgrip to fatigue, and post‐exercise circulatory arrest (PECA). A subset of subjects (n=5) had measurements of muscle sympathetic nerve activity (MSNA). Assessments were done before (PRE) and after (POST) a 6‐week rhythmic handgrip training program (5 days/week, 30% of maximal voluntary contraction, 2 sets of 30 repetitions/min until fatigue). HR was higher at fatigue compared to BL (PRE BL: 65±8 vs 96±20 beats/min, p<0.01) but was not different PRE vs POST (POST BL: 61±7 beats/min). SBP was higher at fatigue and during PECA than during BL (PRE BL: 126±11 vs 168±13 vs 154±12 mmHg, both p<0.01) and was lower POST (main effect, p<0.05). DBP was also higher at fatigue and during PECA (PRE BL: 64±5 vs 90±17 vs 78±8 mmHg, both p<0.05) and tended to be lower POST (main effect, p=0.075). Indices of MSNA were higher during fatigue compared to BL (burst frequency, PRE BL: 11±9 vs 42±29 bursts/min, p<0.01; burst incidence, PRE BL: 17±13 vs 45±23 bursts/100 heart beats, p<0.05) but were no different from PRE to POST (burst frequency, POST BL: 12±10 bursts/min; burst incidence, POST BL: 18±15 bursts/100 heart beats). Maximal voluntary contraction was unchanged after training (52±6 vs 50±5 kg, p=NS); however, time to fatigue was delayed POST training (141.4±32.6 vs 176.4±42.3 sec, p<0.05). After 6 weeks of rhythmic handgrip training we found improvements in cardiovascular parameters and a delay in the onset of fatigue but no change in MSNA indices or strength.Support or Funding InformationSupported by the Faculty Grant Program at Northern Arizona University