Transient dehydration combined with heat stress during calisthenics increased plasma volume by an additional 4% at 24 hours compared to exercise in the heat while euhydrated.
RCT (n=10)
Randomized crossover
No
Does exogenous heat stress and dehydration additively potentiate acute (24 h) cardiovascular and hematological outcomes following orthostatically-stressful calisthenics exercise in healthy individuals?
Effect estimate: Mean difference 4% (95% CI 1-8)
Absolute Event Rate: 11% vs 7%
p-value: p=0.005
Exercise and exogenous heat each stimulate multiple adaptations, but their roles are not well delineated, and that of the related stressor, dehydration, is largely unknown. While severe and prolonged hypohydration potentially "silences" the long-term heat acclimated phenotype, mild and transient dehydration may enhance cardiovascular and fluid-regulatory adaptations. We tested the hypothesis that exogenous heat stress and dehydration additively potentiate acute (24 h) cardiovascular and hematological outcomes following exercise. In a randomized crossover study, 10 physically-active volunteers (mean SD: 173 11 cm; 72.1 11.5 kg; 24 3 year; 6 females) completed three trials of 90-min orthostatically-stressful calisthenics, in: (i) temperate conditions (22 C, 50% rh, no airflow; CON); (ii) heat (40 C, 60% rh) whilst euhydrated (HEAT), and (iii) heat with dehydration (no fluid 16 h before and during exercise; HEAT+DEHY). Using linear mixed effects model analyses, core temperature (T CORE ) rose 0.7 C more in HEAT than CON (95% CL: 0.5, 0.9; p < 0.001), and another 0.4 C in HEAT+DEHY (0.2, 0.5; p < 0.001, vs. HEAT). Skin temperature also rose 1.2 C more in HEAT than CON (0.6, 1.8; p < 0.001), and similarly to HEAT+DEHY (p = 0.922 vs. HEAT). Peak heart rate was 40 bmin -1 higher in HEAT than in CON (28, 51; p < 0.001), and another 15 bmin -1 higher in HEAT+DEHY (3, 27; p = 0.011, vs. HEAT). Mean arterial pressure at 24-h recovery was not consistently below baseline after CON or HEAT (p 0.452), but was reduced 4 1 mm Hg after HEAT+DEHY (0, 8; p = 0.020 vs. baseline). Plasma volume at 24 h after exercise increased in all trials; the 7% increase in HEAT was not reliably more than in CON (5%; p = 0.335), but was an additional 4% larger after HEAT+DEHY (1, 8; p = 0.005 vs. HEAT). Pooled-trial correlational analysis showed the rise in T CORE predicted the hypotension (r = -0.4) and plasma volume expansion (r = 0.6) at 24 h, with more hypotension reflecting more plasma expansion (r = -0.5). In conclusion, transient dehydration with heat potentiates short-term (24-h) hematological (hypervolemic) and cardiovascular (hypotensive) outcomes following calisthenics.
Akerman et al. (Mon,) conducted a rct in Healthy (n=10). Calisthenics in heat with dehydration (HEAT+DEHY) vs. Calisthenics in heat while euhydrated (HEAT) was evaluated on Plasma volume expansion at 24 hours (Mean difference 4%, 95% CI 1-8, p=0.005). Transient dehydration combined with heat stress during calisthenics increased plasma volume by an additional 4% at 24 hours compared to exercise in the heat while euhydrated.