Effect of Handgrip Training in Extreme Heat on the Development of Handgrip Maximal Isometric Strength among Young Males

Abstract

The aim of this study was to evaluate the acute and adaptive effects of passive extreme heat (100 ± 3 °C) exposition in combination with a strength training protocol on maximal isometric handgrip strength. Fifty-four untrained male university students participated in this investigation. Twenty-nine formed the control group (NG) and 25 the heat-exposed group (HG). All the participants performed a 3-week isotonic handgrip strength training program twice a week with a training volume of 10 series of 10 repetitions with 45-s rest between series, per session. All the subjects only trained their right hand, leaving their left hand untrained. HG performed the same training protocol in hot (100 ± 3 °C) conditions in a dry sauna. Maximal isometric handgrip strength was evaluated each training day before and after the session. NG participants did not experience any modifications in either hand by the end of the study while HG increased maximal strength values in both hands (p < 0.05), decreased the difference between hands (p < 0.05), and recorded higher values than the controls in the trained (p < 0.05) and untrained (p < 0.01) hands after the intervention period. These changes were not accompanied by any modification in body composition in either group. The performance of a unilateral isotonic handgrip strength program in hot conditions during the three weeks induced an increase in maximal isometric handgrip strength in both hands without modifications to bodyweight or absolute body composition.

Keywords: handgrip; heat acclimation; isometric strength; performance; strength training.

Figure 1

Representation of the daily intervention followed by the participants.

Figure 2

Strength evolution of both trained (right) and untrained (left) hands during the study. The continuous (hyperthermia) and the discontinuous (normothermia) lines represent the evolution of strength in basal (pre-exercise) conditions. Wilcoxon Test: Pre-post differences of each day in each group: * p < 0.05; ** p < 0.01; Pre-pre differences between consecutive days for each group: ^ p < 0.05; ^^ p < 0.01. Mann–Whitney U Test: Differences between groups at each time point: + p < 0.05; ++ p < 0.01.

Figure 3

Representation of fatigue in both hands as well as the evolution of the differences between hand strength during the study. The filled (hyperthermia) and empty (normothermia) columns represent the evolution of strength in basal (pre-exercise) conditions. Mann–Whitney U Test: Differences between groups at each time point: + p < 0.05; ++ p < 0.01; +++ p < 0.001.

Figure 4

Evolution of internal and external temperatures during the study. The continuous (hyperthermia) and the discontinuous (normothermia) lines represent the evolution of strength in basal (pre-exercise) conditions. Wilcoxon Test: Pre-post differences of each day in each group: * p < 0.05; ** p < 0.01; *** p < 0.001. Mann–Whitney U Test: Differences between groups at each time point: + p < 0.05; ++ p < 0.01; +++ p < 0.001.