Decrease in work rate in order to keep a constant heart rate: biomarker of exercise intolerance following a 10-day bed rest, 2022, Baldassarre et al

Abstract

Aerobic exercise prescription is often set at specific heart rate (HR) values. Previous studies demonstrated that during exercise carried out at a HR slightly above that corresponding to the gas exchange threshold (GET), work rate (WR) has to decrease in order to maintain HR constant. We hypothesized a greater WR decrease at a fixed HR following simulated microgravity/inactivity (bed rest, BR).

Ten male volunteers (23±5 yr) were tested before (PRE) and after (POST) a 10-day horizontal BR, and performed on a cycle ergometer: a) incremental exercise; b) 15-min HRCLAMPED exercise, in which WR was continuously adjusted to maintain a constant HR, corresponding to that at 120% of GET determined in PRE; c) two moderate-intensity constant WR (MOD) exercises. Breath-by-breath VO2, HR and other variables were determined.

After BR, VO2peak and GET significantly decreased, by about 10%. During HRCLAMPED (145±11 b∙min-1), the decrease in WR needed to maintain a constant HR was greater in POST vs. PRE (-39±10 vs. -29±14%, p<0.01). In 6 subjects the decreased WR switched from the heavy- to the moderate-intensity domain. The decrease in WR during HRCLAMPED, in PRE vs. POST, was significantly correlated with the VO2peak decrease (R2=0.52; p=0.02). A greater amplitude of the slow component of the HR kinetics was observed during MOD following BR. Exercise at a fixed HR is not associated with a specific WR or WR domain; the problem, affecting exercise evaluation and prescription, is greater following BR. The WR decrease during HRCLAMPED is a biomarker of exercise intolerance following BR.

Paywall, https://journals.physiology.org/doi/abs/10.1152/japplphysiol.00052.2022

 

This is likely a function of reduced circulating blood volume.

 

Healthy people after bedrest are not comparable to people with ME. We are not deconditioned and even people in the community who are healthy but deconditioned can't be compared to people who are horizontal for 10 days.

I have a feeling this will be used to show that people with ME and longcovid are just deconditioned and need GET