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Impact of Physical Load on Aerobic Exercise Performance during Heat Stress.

Kenefick, Robert W.; Heavens, Kristen R.; Luippold, Adam J.; Charkoudian, Nisha; Schwartz, Steven A.; Cheuvront, Samuel N.
Medicine & Science in Sports & Exercise: Post Acceptance: July 31, 2017
doi: 10.1249/MSS.0000000000001392
Original Investigation: PDF Only

Heavy external loads and heat exposure can negatively impact exercise performance.

Independent effects of heat and load have been studied previously; however the combined effects remain unknown.

Purpose: To investigate the impact of increasing external loads on 5 km treadmill time trial (TT) performance in 20[degrees]C (Temp) and 40[degrees]C (Hot) environmental conditions and to construct an ecologically relevant performance prediction decision-aid.

Methods: 26 male and 4 female volunteers (age 23.5 +/- 6.9 years, weight 76.0 +/- 8.9 kg, height 1.75 +/- 0.07 m; VO2peak, 50.7 +/- 4.5 ml/kg/min) participated in a counter-balanced, mixed model design with each subject assigned to a load group (20%, 30%, or 50% body mass (BM); n=10 per group). Volunteers performed 3, self-paced 5km familiarization time trials (TT) (treadmill) without external load. Each volunteer then performed a 5 km TT in each environment with loads of either 20% (n=10), 30% (n=10) or 50% (n=10) body weight.

Results: 1) loads of (20%, 30% and 50% of BM) impaired 5 km TT performance compared that when unloaded (P<0.05); 2) the time penalties of the 20% and 30% load were < 50% load (P<0.05); 3) in all trials, addition of heat exposure reduced 5 km TT performance beyond the penalty of load itself (P<0.05); 4) the combination of heat and 50% load resulted in a substantial penalty such that continuous work was not sustainable for all of the volunteers.

Conclusions: Relative to prediction models using fixed or constant workload exercise trials, an ecologically valid decision-aid was developed from self-paced data, in which pace (km/hr) can be predicted for individual levels of heat, load, or heat + load in combination.

(C) 2017 American College of Sports Medicine