Muscle oxygen saturation and perceived exertion at moderate intensity: a comparative study between treadmill, elliptical, and cycle

Abstract

Muscle oxygen saturation (SmO₂) is the balance between oxygen supply and demand measured in a local muscle (Pilotto et al., 2022). Understanding the acute dynamic changes in SmO₂ and perceived exertion (RPE) in response to different exercise modalities is crucial for optimising exercise prescription and training outcomes. However, the influence of exercise mode on SmO₂ and RPE remains unclear. This study aimed to assess the acute SmO₂ responses in the gastrocnemius medialis (GM) and vastus lateralis (VL) muscles, and the RPE during treadmill, elliptical and cycle exercises, at identical percentages of heart rate reserve (% HRR).

Fourteen healthy volunteers (8 males/6 females, age:34.9±9.1years) performed exercise on three different ergometers at 50% HRR for 5-minute periods. The Tanaka formula (208-0.7×age) was used to estimate maximal HR. SmO₂ was continuously measured using a near-infrared spectroscopy device (MOXY) placed on the GM and VL muscles. A HR monitor (Garmin) was used to assess the cardiovascular intensity during the session, and the RPE was reported immediately after each exercise period using the Borg Scale (6-20). The SmO₂-related variables, such as average (SmO_2avg), minimum (SmO_2min), and variation (ΔSmO_2min) were determined. Results showed that for the same cardiovascular effort, a significant effect of exercise mode was found in SmO_2avg (χ²(2)=18.436, p<0.001, in GM), SmO_2min (χ²(2)=8.769, p=0.012 and χ²(2)=15.857, p<0.001, in VL and GM, respectively), and ΔSmO_2min (χ²(2)=8.769, p=0.012 and χ²(2)=15.857, p<0.001, in VL and GM, respectively). All these variables were significantly different between the cycle and treadmill, with lower SmO_2min and higher ΔSmO_2min values reached during the cycle in the VL (p=0.014, for both variables) while in GM (p<0.001, for both variables), the same results were observed for the opposite (i.e., treadmill). Only GM showed a significantly lower SmO_2avg during the treadmill compared to the cycle (p<0.001). There were no significant differences in SmO₂-related variables between cycle and elliptical or between elliptical and treadmill in both muscles. RPE was significantly different between exercise modes (χ²(2)=8.857, p=0.012), with a higher RPE in the cycle compared to elliptical (p=0.049) and treadmill (p=0.042). These findings highlight the distinct SmO₂ and RPE responses elicited by different exercise modes, even at equal cardiovascular intensity. The cycle exercise induced a higher response of SmO₂ in VL, while the treadmill elicited a higher response of SmO₂ in the GM muscle. This reinforced the importance of considering exercise mode when designing and optimising training programs to target specific muscle groups and achieve desired physiological responses.