Energy cost and lower leg muscle activities during erect bipedal locomotion under hyperoxia

Abstract

BackgroundEnergy cost of transport per unit distance (CoT) against speed shows U-shaped fashion in walking and linear fashion in running, indicating that there exists a specific walking speed minimizing the CoT, being defined as economical speed (ES). Another specific gait speed is the intersection speed between both fashions, being called energetically optimal transition speed (EOTS). We measured the ES, EOTS, and muscle activities during walking and running at the EOTS under hyperoxia (40% fraction of inspired oxygen) on the level and uphill gradients (+ 5%).MethodsOxygen consumption and carbon dioxide output were measured to calculate the CoT values at eight walking speeds (2.4–7.3 km h−1) and four running speeds (7.3–9.4 km h− 1) in 17 young males. Electromyography was recorded from gastrocnemius medialis, gastrocnemius lateralis (GL), and tibialis anterior (TA) to evaluate muscle activities. Mean power frequency (MPF) was obtained to compare motor unit recruitment patterns between walking and running.Results, , and CoT values were lower under hyperoxia than normoxia at faster walking speeds and any running speeds. A faster ES on the uphill gradient and slower EOTS on both gradients were observed under hyperoxia than normoxia. GL and TA activities became lower when switching from walking to running at the EOTS under both FiO2 conditions on both gradients, so did the MPF in the TA.ConclusionsES and EOTS were influenced by reduced metabolic demands induced by hyperoxia. GL and TA activities in association with a lower shift of motor unit recruitment patterns in the TA would be related to the gait selection when walking or running at the EOTS.Trial registrationUMIN000017690 (R000020501). Registered May 26, 2015, before the first trial.Electronic supplementary materialThe online version of this article (10.1186/s40101-018-0177-7) contains supplementary material, which is available to authorized users.

Peer Review #3 of "Why do we transition from walking to running? Energy cost and lower leg muscle activity before and after gait transition under body weight support (v0.3)"

“…These results were equivalent to those of our recent studies that measured TA activity during walking and running at the EOTS (Abe, Fukuoka & Horiuchi, 2017;Abe et al, 2018), which suggested that the motor unit recruitment pattern of the TA shifted more toward Type I (slow twitch) fibers rather than Type II (fast twitch) fibers after the walk-run transition. Several studies have also reported that an abrupt increase in TA activity associated with the walk-run transition (Hreljac, 1995;Hreljac et al, 2008;Bartlett & Kram, 2008;Malcolm et al, 2009;Shih et al, 2016).…”

“…An abrupt increase in muscle activity of the dorsiflexor (tibialis anterior; TA) has been observed when participants walked at a speed close to the PTS (Hreljac, 1995;Hreljac et al, 2008;Prilutsky & Gregor, 2001; Bartlett & Kram, 2008;Malcolm et al, 2009;Shih et al, 2016), and our recent studies showed muscle activity of the TA decreased when participants switched from walking to running at the EOTS (Abe, Fukuoka & Horiuchi, 2017;Abe et al, 2018). In association with a decrease in TA activity when switching the gait pattern, mean power frequency (MPF; Hz) of the TA became lower, suggesting that more Type 1 muscle fibers were recruited in the TA during running than walking at the EOTS.…”

“…An alteration of the MPF values between walking and running allows us to evaluate muscle fiber recruitment pattern in each gait. The sum of the rectified EMG (µV•sec) was normalized by measured time (sec) and number of steps to cancel the effects of step frequency (Abe, Fukuoka & Horiuchi, 2017;Abe et al, 2018). The EMG values obtained were further normalized to those obtained at 1.11 m•s −1 under each condition.…”

Why do we transition from walking to running? Energy cost and lower leg muscle activity before and after gait transition under body weight support

“…An abrupt increase in muscle activity of the dorsiflexor ( tibialis anterior ; TA) has been observed when participants walked at a speed close to the PTS (Hreljac, 1995; Hreljac et al, 2008; Prilutsky & Gregor, 2001; Bartlett & Kram, 2008; Malcolm et al, 2009; Shih et al, 2016), and our recent studies showed muscle activity of the TA decreased when participants switched from walking to running at the EOTS (Abe, Fukuoka & Horiuchi, 2017; Abe et al, 2018). In association with a decrease in TA activity when switching the gait pattern, mean power frequency (MPF; Hz) of the TA became lower, suggesting that more Type I muscle fibers were recruited in the TA during running than walking at the EOTS.…”

“…An alteration of the MPF values between walking and running allows us to evaluate muscle fiber recruitment pattern in each gait. The sum of the rectified EMG (µV·s) was normalized by measured time (s) and number of steps to cancel the effects of step frequency (Abe, Fukuoka & Horiuchi, 2017; Abe et al, 2018). The EMG values obtained were further normalized to those obtained at 1.11 m·s −1 under each condition.…”