The interplay between gastrocnemius medialis force–length and force–velocity potentials, cumulative EMG activity and energy cost at speeds above and below the walk to run transition speed

Abstract

The aim of this study was to investigate the interplay between the force-length (F-L) and force-velocity (F-V) potentials of gastrocnemius medialis (GM) muscle fascicles, the cumulative muscle activity per distance travelled (CMAPD) of the lower limb muscles (GM, vastus lateralis, biceps femori, tibialis anterior) and net energy cost (C net ) during walking and running at speeds above and below the walk-to-run transition speed (walking: 2-8 km h −1 ; running: 6-10 km h −1 ). A strong association was observed between C net and CMAPD: both changed significantly with walking speed but were unaffected by speed in running. The F-L and F-V potentials decreased with speed in both gaits and, at 6-8 km h −1 , were significantly larger in running. At low to moderate walking speeds (2-6 km h −1 ), the changes in GM force potentials were not associated with substantial changes in CMAPD (and C net ), whereas at walking speeds of 7-8 km h −1 , even small changes in force potentials were associated with steep increases in CMAPD (and C net ). These data suggest that: (i) the walk to run transition could be explained by an abrupt increase in C net driven by an upregulation of the EMG activity (e.g., in CMAPD) at sustained walking speeds (>7 km h −1 ) and (ii) the reduction in the muscle's ability to produce force (e.g., in the F-L and F-V potentials) contributes to the increase in CMAPD (and C net ). Switching to running allows regaining of high force potentials, thus limiting the increase in CMAPD (and C net ) that would otherwise occur to sustain the increase in locomotion speed.

Impairments in muscle shape changes affect metabolic demands duringin-vivocontractions

“…Therefore, GM muscle fascicle operated at a very high F-L potential in all conditions. These small differences are not expected to provide any sizeable effect on metabolic energy expenditure [6,30].…”

“…Hill [4] generalized the effects of velocity into the well-known F-V relationship, explaining that the muscle's force potential decreases with increasing shortening velocity. Hence, operating at a higher F-V potential for a given mechanical request allows the muscle to generate high force with a lower contraction velocity, thus reducing metabolic energy expenditure [5,6]. It is, therefore, possible to conclude that mechanisms able to modify the F-V potential of a given muscle could affect metabolic energy expenditure as well as contraction efficiency since, for a given mechanical output, an increase in fascicle shortening velocity affects the fascicle operating range along the efficiency-velocity relationship.…”

Energetics (and Mechanical Determinants) of Sprint and Shuttle Running

“…quasi-isometric struts developing force at favorable regions of the force-velocity and force-length relationships [61][62][63][64]. On the contrary, during short shuttle distances covered at high speed or at the start of a maximal sprint, the lower limb's MTUs must operate in a motor-like manner to generate net positive mechanical energy.…”

Muscle fibre typology affects whole‐body metabolic rate during isolated muscle contractions and human locomotion

“…Another potentially powerful approach to study the effect of fibre type distribution on whole body metabolic rate is to compare walking and running at a speed close to the walk‐to‐run transition speed. Although walking and running at 2 m/s have comparable whole‐body metabolic rates (Farris & Sawicki, 2012a), walking requires substantially faster triceps surae muscle contractions but lower triceps surae peak forces than running at 2 m/s (Farris & Sawicki, 2012b; Lai et al., 2015; Monte et al., 2023). The triceps surae muscles are major energy consumers during both walking and running and the reduced contraction velocity when switching from walking to running has been suggested to be an important trigger to transition from walking to running (Farris & Sawicki, 2012b; Monte et al., 2023).…”

“…Although walking and running at 2 m/s have comparable whole‐body metabolic rates (Farris & Sawicki, 2012a), walking requires substantially faster triceps surae muscle contractions but lower triceps surae peak forces than running at 2 m/s (Farris & Sawicki, 2012b; Lai et al., 2015; Monte et al., 2023). The triceps surae muscles are major energy consumers during both walking and running and the reduced contraction velocity when switching from walking to running has been suggested to be an important trigger to transition from walking to running (Farris & Sawicki, 2012b; Monte et al., 2023). Hence, if muscle fibre typology affects whole‐body metabolic rate, we expect that individuals with a predominance of slow muscle fibres would exhibit a higher ratio of metabolic energy consumption during walking versus running at 2 m/s compared to individuals who demonstrate a rather fast muscle fibre typology.…”