Gastrocnemius Medialis and Vastus Lateralis in vivo muscle‐tendon behavior during running at increasing speeds

Abstract

This study combines in vivo ultrasound measurements of the Vastus Lateralis (VL) and Gastrocnemius Medialis (GM) muscles with electromyographic, kinematic, and kinetic measurements during treadmill running at different speeds (10, 13, and 16 km/h) to better understand the role of muscle and tendon behavior in two functionally different muscle‐tendon units. In addition, the force‐length and force‐velocity relationships of VL and GM were experimentally assessed by combining dynamometry and EMG data with ultrasound measurements. With increasing running speed, the operating length of the fascicles in the stance phase shifted toward smaller lengths in the GM (P < .05; moving down the ascending limb of the F‐L relationship) and longer lengths in the VL (P < .05; moving down the descending limb) at all speeds; however, both muscles contracted close to their optimal length L0, where isometric force is maximal. Whereas the length of VL SEE did not change as a function of speed, GM SEE lengthened and shortened more at higher speeds. With increasing running speed, the contribution of elastic strain energy to the positive power generated by the MTU increased more for GM (from 0.75 to 1.56 W/kg) than for VL (from 0.62 to 1.02 W/kg). Notwithstanding these differences, these results indicate that, at increasing running speeds, both the VL and GM muscles produce high forces at low contraction velocities, and that the primary function of both muscle‐tendon units is to enhance the storage and recovery of elastic strain energy.

The influence of Achilles tendon mechanical behaviour on “apparent” efficiency during running at different speeds

“…Based on these theoretical considerations, if the whole muscle-tendon unit length changes could be attributed to the tendon only, the muscle fibres would operate under isometric conditions, reducing the fascicle length changes (and, therefore, the mechanical work done by the muscles) and the level of muscle activation required for a given force (Fletcher and MacInthos 2017). These theoretical notions were supported by recent studies of Bohm et al (2019) and Monte et al (2020), which revealed that the plantar flexor muscles operated quasi-isometrically at a high-force potential during running at different speeds. Furthermore, Bohm and co-workers found a negative significant correlation between the force-length-velocity potential of the soleus muscle and the energy cost of running at 10 km h −1 , suggesting that the higher the force potential the lower the energy expended.…”

“…2) suggests that the elastic energy provided by the Achilles tendon recoil during the propulsive phase would affect the total mechanical work provided by the body. Indeed, as showed by Monte et al (2020) with faster running speed, the GM muscle fascicle operating range shifts towards smaller lengths (on the ascending limb of the F-L relationship) yet operating quasi-isometrically and at a high force potential (> 80% of the maximum isometric force) and this behaviour allows the muscle fascicles to reduce the Fig. 2 Correlations between (positive) tendon work and total mechanical work (at the whole-body level), net energy cost of running and "apparent" efficiency at the three investigated speeds (blue dots: 10 km h −1 , red squares: 13 km h −1 , green triangles: 16 km h −1 ).…”

“…This mechanism may be a consequence of the plantar flexor muscle fibres remaining relatively isometric as running speed increases, a behaviour that allows to generate large muscle forces and facilitates the storage and recovery of tendon elastic strain energy. This was recently verified by in vivo studies that analysed the muscle and tendon behaviour of the plantar flexors during running at increasing speed (Lai et al 2018;Werkhausen et al 2019;Monte et al 2020;Bohm et al 2019). For instance, Monte et al (2020) demonstrated that the gastrocnemius medialis muscle fascicles shorten during the entire stance phase, but that the series elastic components accommodate much of the displacement of the MTU, allowing the series elastic components to provide the larger amount of mechanical power of the MTU.…”

“…This was recently verified by in vivo studies that analysed the muscle and tendon behaviour of the plantar flexors during running at increasing speed (Lai et al 2018;Werkhausen et al 2019;Monte et al 2020;Bohm et al 2019). For instance, Monte et al (2020) demonstrated that the gastrocnemius medialis muscle fascicles shorten during the entire stance phase, but that the series elastic components accommodate much of the displacement of the MTU, allowing the series elastic components to provide the larger amount of mechanical power of the MTU. This result suggests that fibres in distal limb muscles, such as the ankle plantar flexors, act like isometric struts to facilitate greater storage and recovery of tendon elastic strain energy at fast locomotion speeds (as indicated by Biewener and Roberts 2000).…”

“…During different forms of locomotion (e.g. walking and running), the elastic elements could accommodate the largest part of the MTU length changes, allowing the fascicles to work at a high force–length–velocity potential (Fukunaga et al 2001 ; Lichtwark et al 2007 ; Bohm et al 2019 ; Monte et al 2020 ). Without tendons, the fascicle shortening velocity would be higher, increasing the cross-bridge turnover and the energy demand for muscle contraction (Woledge et al 1985 ).…”