How Does the Body Respond to Passive Physical Activity? Cortisol and Salivary Alpha-amylase During Active and Passive Cycling

Background and/or Objectives: Physical activity (PA) has been shown to be beneficial in the regulation of stress hormones and modifying the stress pathway. However, many individuals face barriers to participating in PA, such as musculoskeletal injuries, neuromuscular disorders, spinal cord injuries, or brain trauma. One potential intervention for those individuals is passive PA, defined as the movement of the body without muscle engagement or voluntary effort. There is a poor understanding of the physiological response to passive PA and how it compares to the response to active PA. In particular cortisol and salivary alpha-amylase (sAA), hormones implicated in the stress response, are known to be altered by active PA. This study aimed to investigate if these hormones are similarly influenced by passive cycling.

Design: experimental, prospective, within subjects study

Setting: in lab room, AC controlled temperature

Participants: Thirty-five healthy, young adults (13 males, Mean age= 21.20 ± 2.93)

Interventions: Active cycling: participants provided force to cycle. Passive cycling: participant's feet and ankles were affixed to the cycle and a motor moved their limbs.

Main Outcome Measures: Saliva cortisol and salivary alpha amylase levels from 3 different time points in condition (pre-cycling, post-cycling, and 30 minutes post-cycling). Enjoyment of participant via PACES questionnaire.

Results: Paired t-tests revealed no significant difference in cortisol and sAA levels between the active and passive conditions (p>.08). Enjoyment of active (94.13 ± 15.87) and passive (88.81 ± 21.94) cycling did not differ significantly (p=0.109).

Conclusions: The changes in hormones in response to active PA were not significantly different from the changes in hormones in passive PA, therefore, making passive PA a potential therapeutic intervention that yields similar physiological effects on the stress pathway and similar levels of enjoyment as active PA.