ECSS Paris 2023: OP-BM17
INTRODUCTION: During locomotion, running is generally more metabolically costly than walking at similar speed [1]. The metabolic cost (Mc) is primarily determined by the ATP required to produce force [2]. Mc is thus modulated by a muscles ability to produce force in response to muscle activation (fability), as well as the velocity of contraction and muscle length [3]. However, the interplay between these mechanisms to explain why walking is a more economical mode of locomotion than running remains unclear. The aim of this study was to determine how different lower limb muscle recruitment and fability, during walking and running determine differences in Mc. METHODS: Eleven endurance runners (60.5 ± 7.1 kg; 169.0 ± 6.6 cm; 23.6 ± 3.3 y) performed two 6-minutes walking and running trials on a motorized instrumented treadmill (Bertec) at a constant speed of 1.75 m/s. The kinematics were recorded with nine optoelectronic cameras. Electromyography (EMG) data from eight knee and ankle muscles, kinetics and kinematics were integrated into an EMG-driven model proceeding by inverse dynamics to estimate locomotor muscle fability and force. Mc was estimated by indirect calorimetry from the expired gas. Comparisons between walking and running were made for Mc, and integral and maximal values of force and fability during the locomotion cycle using parametric statistical mapping. RESULTS: The Mc of running was 34% higher than walking (d = 3.0). The rectus femoris, vastus medialis, vastus intermedius and vastus lateralis produced more force during propulsion during running than during walking, despite similar fability. The soleus, during propulsion, and the tibialis anterior, during braking, produced more force during walking, however, these forces were produced with a greater fability integral (i.e. contraction generating more force but under more economical conditions). Positive correlations were found between Mc and the force integral of the tibialis anterior (r = 0.72, p = 0.005) for walking, and negative correlations between Mc and the fability integral of the vastus lateralis (r = -0.52, p = 0.049) and vastus intermedius (r = -0.56, p = 0.036) for running. CONCLUSION: The greater force produced by the knee extensors, particularly during braking and propulsion, where producing force is costly, contribute to the greater Mc during running, compared to walking. The greater force of the tibialis anterior and soleus during walking does not increase the Mc of this mode of locomotion, as it is produced economically. Transposing force production patterns of walking, which appears energetically efficient, with those of running may offer a strategy to reduce Mc and enhance running performance. [1] Monte et al., Exp Physiol (2023) [2] Riddick et Kuo, Sci Rep (2022) [3] Sasaki et Neptune, J Biomech (2006)
Read CV Clément LemineurECSS Paris 2023: OP-BM17
INTRODUCTION: Wind drag impacts how athletes run and how much energy they spend to do it. With headwind, runners increase their positive center of mass work and reduce frontal area, while they increase negative work with tailwind (1). However, it is unclear how these adjustments affect the metabolic cost of running and the activity of individual muscles. Understanding it would shed light on how humans adapt their locomotion to external forces, how well treadmill experiments can be generalized to outdoor conditions, and how much air drag impacts athletes’ performance. This study investigated how wind-induced drag affects the metabolic cost and the activity of lower limb muscles during running. METHODS: Eight male endurance athletes (age: 32±6 y, mass: 63.2±6.6 kg; height: 1.77±0.05 m, personal best 10000 m: 31:20±01:12 min:s) ran at 4.0 m/s on an instrumented treadmill in a wind tunnel, where tail- and headwind speeds ranged from 0 to 12.5 m/s. Metabolic cost, in J/(kg m), was measured via gas exchange analysis. Electromyographic activity (Delsys, 1kHz) was recorded unilaterally from erector spinae, gluteus maximus, gluteus medius, vastus lateralis, vastus medialis, rectus femoris, sartorius, tensor fasciae latae, adductor longus, biceps femoris, semitendinosus, gastrocnemius lateralis, gastrocnemius medialis, peroneus longus, and tibialis anterior; the average activity per unit distance was then computed (2). Drag force was calculated as the average horizontal ground reaction force over an integral number of strides (1). Mixed effects models regressed metabolic cost and muscle activities against drag force; for each muscle, linear and quadratic models were compared, and the model with the lowest Akaike Information Criterion was chosen. RESULTS: Drag forces ranged from -58 to 53 N, where negative and positive signs indicate tailwind and headwind, respectively. Over such a range, metabolic cost increased linearly with headwind drag and decreased linearly with tailwind drag (cost = 4.0 + 0.04*drag force, conditional R-squared = 0.90). Increasing headwind drag significantly increased the activity of gluteus maximus and gastrocnemius lateralis (p<0.001) while reducing that of gluteus medius (p<0.001); the reverse trends were observed for tailwind. Biceps femoris and peroneus longus activity showed a U-shaped response, their activity being lowest at zero drag and increasing with both head- and tailwind (p < 0.001). The remaining muscles were not significantly affected by wind. CONCLUSION: Metabolic cost increases linearly with headwind drag and decreases linearly with tailwind drag, while lower limb muscles show heterogeneous activation patterns in response to wind. These muscle-specific variations are independent of metabolic cost and may optimize posture, frontal area, or force and work production across wind conditions. REFERENCES : 1) Mesquita et al., J Appl Physiol, 2024 2) Pincheira et al., J Aging Phys Act, 2016
Read CV Francesco LucianoECSS Paris 2023: OP-BM17
INTRODUCTION: Lower-Body Positive Pressure Treadmills (LBPPT) enable fine-grained control over the external load during running. These devices provide body weight support (BWS) through an overpressure in a chamber surrounding the athletes and running surfaces. Previous research on the effects of BWS on running biomechanics revealed changes in spatiotemporal (1) and kinematic variables (2). However, most studies neither provided sex-specific analyses nor included nonlinear running stability, a measure for locomotor control capabilities. Biomechanics and running injury epidemiology differ between sexes (3, 4). Hence, this work aimed to investigate how BWS affects running biomechanics in male and female athletes. METHODS: Twenty-six competitive distance runners (15 female, age: 33.6±9.8 years, BMI: 21.6±2.4 kg⸱m-2) completed one running session on an LBPPT (AlterG 500 Pro). Following a familiarisation period, the experimental protocol consisted of nine running bouts at randomly ordered unloading stages of 0 – 80% BWS in steps of 10%. Each bout lasted three minutes at 12 km/h with no rest in between. We measured plantar pressure with two pressure-sensing insoles (200Hz, loadsol, novel) as well as acceleration and angular velocity at the right foot and right tibia using inertial measurement units (500Hz, ICM-20601, TDK InvenSens). We calculated stance time, swing time, normalized ground contact time, and maximum plantar force during stance from the insole data. From the inertial sensor data, we calculated peak tibial acceleration and running stability as the largest short-term finite-time divergence exponent λs (5). Linear mixed-effects models were used to investigate the effects of BWS, sex, and their interaction on all biomechanical variables. RESULTS: All variables were significantly affected by increasing BWS with the largest effects for reduced maximum plantar force (β=-0.81 [-0.86 to -0.76], p<0.001), increased swing time (β=0.74 [0.67 to 0.82], p<0.001), and decreased normalized ground contact time (β=-0.61 [-0.66 to -0.56], p<0.001). Running stability decreased at the tibia (β=0.10 [0.02 to 0.17], p=0.009) but increased at the foot (β=-0.12 [-0.22 to -0.02], p=0.017). There were no significant BWS*sex interaction effects among the variables under investigation. CONCLUSION: Our results confirm previous studies showing reduced external load metrics and changes in spatiotemporal running patterns with increasing BWS. Running stability was also affected by BWS but the small effect sizes question its practical relevance. We showed that despite overall differences between male and female runners’ technique, both sexes respond similarly to BWS. These are important findings especially for practitioners when planning return-to-sport programs with an LBPPT available. REFERENCES: 1. Neal et al., J Orthop Sports Phys Ther. 2016 2. Hodges-Long et al., Phys Ther Sport. 2020 3. Hollander et al., Sports Med. 2021 4. Xie et al., Front Physiol. 2022 5. Hoenig et al., Eur J Sport Sci. 2019
Read CV Dominik FohrmannECSS Paris 2023: OP-BM17