Introduction: Passive heating (PH) has been proposed as a potential exercise (E) mimetic
strategy showing acute and chronic effects on skeletal muscle adaptation in people who are
unable to perform or complete sufficient exercise. Like exercise, heating increases heart
rate (HR), peripheral artery blood flow and provokes a thermoregulatory response.
Purpose: The aim of our study was to compare the acute metabolic, cardiovascular and
respiratory response to passive heating and to compare it with the response to HR- and
duration-matched cycling. Methods: In a fixed crossover designed study, 10 healthy
participants (22,4 ± 0,5 yr) underwent 30 min of whole-body passive heating (55 °C in an
infrared sauna), followed by 30 min of manually load managed cycling on a separate day.
Cycling load was added in steps to comply with the same HR time profile as obtained
during PH. HR, arterial blood pressure (ABP), oxygen consumption (VO2), respiratory
quotient (R), ventilation (VE), and sublingual temperature (Tsl) were measured
continuously during PH and E (Finapres Ohmeda, Cosmed quark CPET, Perimed
PeriFlux5001). Based on metabolic measurements, stroke volume (SV) and cardiac output
(CO) were determined. Results: At the end of PH and E HR increased significantly
compared to resting state (p < 0,001) (109,9 (2,3) beats per min versus 74,6 (2,7) beats per
min) and was the same at both procedures. However, other metabolic, respiratory, and
cardiovascular parameters differed statistically significant (p < 0,001) in last 5 minutes
during E compared to last 5 minutes of PH (diastolic ABP: 91,8 (15,7) mmHg (E)
compared to 84,9 (6,2) mmHg (PH); systolic ABP: 159,1 (8,5) mmHg (E) compared to
117,7 (7,2) mmHg (PH); VO2: 1141,2 (209,9) mL/min (E) compared to 339,6 (21,2)
mL/min (PH); R: 0,87 (0,02) (E) compared to 0,82 (0,01) (PH); VE: 30,2 (5,3) L/min (E)
compared to 11,5 (1,6) L/min (PH); Tsl: 36,6 (0,7) gradC (E) compared to 37,4 (0,4) gradC
(PH); SV: 10,1 (0,6) arbitrary units (E) compared to 3,3 (0,1) arbitrary units (PH); CO:
1122,5 (204,5) arbitrary units (E) compared to 366,8 (48,4) arbitrary units (PH)).
Discussion and conclusion: Passive heating has shown some potential benefits for skeletal
muscle mass gain and muscle force improvement however passive heating provoked
minimal cardiovascular, respiratory, and metabolic responses compared to HR- and
duration-matched exercise on cycloergometer. It might be a worthwhile alternative to be
recommended as an exercise mimetic for those people who lack or are unable to complete
sufficient exercise.
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