An in-silico investigation of the effect of changing cycling crank power and cadence on muscle energetics and active muscle volume.

This study used musculoskeletal modelling to explore the relationship between cycling conditions (power output and cadence) and muscle activation and metabolic power. We hypothesized that the cadence that minimized the simulated average active muscle volume would be higher than the cadence that minimized the simulated metabolic power. We validated the simulation by comparing the predicted muscle activation and fascicle velocities with experimental electromyography and ultrasound images.

Individualization of Footwear for Optimizing Running Economy: A Theoretical Framework.

Advanced footwear technologies contain thicker, lightweight, and more resilient midsoles and are associated with improved running economy (RE) compared with traditional footwear. This effect is highly variable with some individuals gaining a greater RE benefit, indicating that biomechanics plays a mediating role with respect to the total effect. Indeed, the energy generated by contractile elements and the elastic energy recovered from stretched tendons and ligaments in the legs and feet are likely to change with footwear.

Increased force and elastic energy storage are not the mechanisms that improve jump performance with accentuated eccentric loading during a constrained vertical jump.

Accentuated eccentric loading (AEL) involves higher load applied during the eccentric phase of a stretch-shortening cycle movement, followed by a sudden removal of load before the concentric phase. Previous studies suggest that AEL enhances human countermovement jump performance, however the mechanism is not fully understood. Here we explore whether isolating additional load during the countermovement is sufficient to increase ground reaction force, and hence elastic energy stored, at the start of the upward movement and whether this leads to increased jump height or power generation.

Implementation of a passive bi-articular ankle-knee exoskeleton during maximal squat jumping.

Owing to the unexplored potential to harness knee extension power during jumping, the current study aimed to examine how joint mechanics were altered with a biologically inspired, passive bi-articular ankle-knee exoskeleton, which could potentially facilitate greater jump height by increasing work production about the knee and ankle. Twenty-five participants (16 males and 9 females, 175.2 ± 8.

Markerless motion capture provides accurate predictions of ground reaction forces across a range of movement tasks.

Measuring or estimating the forces acting on the human body during movement is critical for determining the biomechanical aspects relating to injury, disease and healthy ageing. In this study we examined whether quantifying whole-body motion (segmental accelerations) using a commercial markerless motion capture system could accurately predict three-dimensional ground reaction force during a diverse range of human movements: walking, running, jumping and cutting. We synchronously recorded 3D ground reaction forces (force instrumented treadmill or in-ground plates) with high-resolution video from eight cameras that were spatially calibrated relative to a common coordinate system.

Validation of a musculoskeletal model for simulating muscle mechanics and energetics during diverse human hopping tasks.

Computational musculoskeletal modelling has emerged as an alternative, less-constrained technique to indirect calorimetry for estimating energy expenditure. However, predictions from modelling tools depend on many assumptions around muscle architecture and function and motor control. Therefore, these tools need to continue to be validated if we are to eventually develop subject-specific simulations that can accurately and reliably model rates of energy consumption for any given task.

It is not just the work you do, but how you do it: the metabolic cost of walking uphill and downhill with varying grades.

The cost of walking and running on uneven terrain is not directly explained by external mechanical work. Although metabolic cost of transport increases linearly with gradient at uphill and downhill gradients exceeding 15%, at shallower gradients, the relationship is nonlinear, with the minimum cost occurring at ∼10% downhill grade. Given these nonlinear relationships between grade and metabolic cost, we projected a significant difference in the total metabolic cost of two walking conditions that required the same total external mechanical work be performed over the same total period of time; in one condition, time was spent walking to gradients that were fixed at +10.

Elastic ankle exoskeletons influence soleus fascicle dynamics during unexpected perturbations.

Spring-based passive ankle exoskeletons have been designed to emulate the energy conservation and power amplification roles of biological muscle-tendon units during locomotion. Yet, it remains unknown if similar assistive devices can serve the other elastomechanical role of biological muscle-tendon units - power attenuation. Here we explored the effect of bilateral passive ankle exoskeletons on neuromuscular control and muscle fascicle dynamics in the ankle plantarflexors during rapid, unexpected vertical perturbations.

The effects of crank power and cadence on muscle fascicle shortening velocity, muscle activation and joint-specific power during cycling.

Whilst people typically choose to locomote in the most economical fashion, during bicycling they will, unusually, chose cadences that are higher than metabolically optimal. Empirical measurements of the intrinsic contractile properties of the vastus lateralis (VL) muscle during submaximal cycling suggest that the cadences that people self-selected might allow for optimal muscle fascicle shortening velocity for the production of knee extensor muscle power. It remains unclear, however, whether this is consistent across different power outputs where the self-selected cadence (SSC) varies.

Linking muscle mechanics to the metabolic cost of human hopping.

Many models have been developed to predict metabolic energy expenditure based on biomechanical proxies of muscle function. However, current models may only perform well for select forms of locomotion, not only because the models are rarely rigorously tested across subtle and broad changes in locomotor task but also because previous research has not adequately characterised different forms of locomotion to account for the potential variability in muscle function and thus metabolic energy expenditure. To help to address the latter point, the present study imposed frequency and height constraints to hopping and quantified gross metabolic power as well as the activation requirements of medial gastrocnemius (MG), lateral gastrocnemius (GL), soleus (SOL), tibialis anterior (TA), vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF), and the work requirements of GL, SOL and VL.

Increased muscle force does not induce greater stretch-induced damage to calf muscles during work-matched heel drop exercise.

Purpose: To investigate the effect of muscle force during active stretch on quantitative and qualitative indicators of exercise-induced muscle damage (EIMD) in the medial gastrocnemius (MG) muscle.

Methods: Twelve recreationally active volunteers performed two trials of an eccentric heel drop exercise. Participants performed a single bout of low-load (body weight) and high-load (body weight + 30% body weight) exercises on separate legs.

The influence of elastic ankle exoskeletons on lower limb mechanical energetics during unexpected perturbations.

Passive elastic ankle exoskeletons have been used to augment locomotor performance during walking, running and hopping. In this study, we aimed to determine how these passive devices influence lower limb joint and whole-body mechanical energetics to maintain stable upright hopping during rapid, unexpected perturbations. We recorded lower limb kinematics and kinetics while participants hopped with exoskeleton assistance (0, 76 and 91 Nm rad) on elevated platforms (15 and 20 cm) which were rapidly removed at an unknown time.

Musculoskeletal simulations to examine the effects of accentuated eccentric loading (AEL) on jump height.

Background: During counter movement jumps, adding weight in the eccentric phase and then suddenly releasing this weight during the concentric phase, known as accentuated eccentric loading (AEL), has been suggested to immediately improve jumping performance. The level of evidence for the positive effects of AEL remains weak, with conflicting evidence over the effectiveness in enhancing performance. Therefore, we proposed to theoretically explore the influence of implementing AEL during constrained vertical jumping using computer modelling and simulation and examined whether the proposed mechanism of enhanced power, increased elastic energy storage and return, could enhance work and power.

Understanding altered contractile properties in advanced age: insights from a systematic muscle modelling approach.

Age-related alterations of skeletal muscle are numerous and present inconsistently, and the effect of their interaction on contractile performance can be nonintuitive. Hill-type muscle models predict muscle force according to well-characterised contractile phenomena. Coupled with simple, yet reasonably realistic activation dynamics, such models consist of parameters that are meaningfully linked to fundamental aspects of muscle excitation and contraction.

The feasibility, validity, and reliability of strain measures in the iliotibial band during isolated muscular contractions.

The iliotibial band (ITB) is a unique anatomical structure that transmits forces from two in-series muscles across the lateral knee. Little is known about how force is transmitted, via ITB strain, in response to muscle activation. We have developed a technique to measure the strain through the distal ITB during isolated contractions of the tensor fascia latae (TFL) muscle, using a Kanade-Lucas-Tomasi ultrasound image tracking algorithm.

Modulations in motor unit discharge are related to changes in fascicle length during isometric contractions.

The integration of electromyography (EMG) and ultrasound imaging has provided important information about the mechanisms of muscle activation and contraction. Unfortunately, conventional bipolar EMG does not allow an accurate assessment of the interplay between the neural drive received by muscles, changes in fascicle length and torque. We aimed to assess the relationship between modulations in tibialis anterior muscle (TA) motor unit (MU) discharge, fascicle length, and dorsiflexion torque using ultrasound-transparent high-density EMG electrodes.

2021 ISB World Athletics Award for Biomechanics: The Subtalar Joint Maintains "Spring-Like" Function While Running in Footwear That Perturbs Foot Pronation.

Humans have the remarkable ability to run over variable terrains. During locomotion, however, humans are unstable in the mediolateral direction and this instability must be controlled actively-a goal that could be achieved in more ways than one. Walking research indicates that the subtalar joint absorbs energy in early stance and returns it in late stance, an attribute that is credited to the tibialis posterior muscle-tendon unit.

Examining the intrinsic foot muscles' capacity to modulate plantar flexor gearing and ankle joint contributions to propulsion in vertical jumping.

Background: During human locomotion, a sufficiently stiff foot allows the ankle plantar flexors to generate large propulsive powers. Increasing foot stiffness (e.g.

Isometric fascicle behaviour of the biceps femoris long head muscle during Nordic hamstring exercise variations.

Objectives: To compare biceps femoris long head (BFlh) muscle tendon unit and fascicle function during Nordic hamstring exercise (NHE) variations with different hip range of motion.

Design: Cross-sectional.

Methods: Twelve healthy volunteers (age: 24 ± 4 years; mass: 77 ± 6 kg; height: 177 ± 4 cm) performed two NHE variations: NHE with hips in neutral (fixed) position (conventional NHE); and NHE with hip flexion/extension.

The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial.

The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared with interventions involving a lower level of load duration and intensity.

Flexor digitorum brevis utilizes elastic strain energy to contribute to both work generation and energy absorption at the foot.

The central nervous system utilizes tendon compliance of the intrinsic foot muscles to aid the foot's arch spring, storing and returning energy in its tendinous tissues. Recently, the intrinsic foot muscles have been shown to adapt their energetic contributions during a variety of locomotor tasks to fulfil centre of mass work demands. However, the mechanism by which the small intrinsic foot muscles are able to make versatile energetic contributions remains unknown.

The effect of small changes in rate of force development on muscle fascicle velocity and motor unit discharge behaviour.

When rate of force development is increased, neural drive increases. There is presently no accepted explanation for this effect. We propose and experimentally test the theory that a small increase in rate of force development increases medial gastrocnemius fascicle shortening velocity, reducing the muscle's force-generating capacity, leading to active motor units being recruited at lower forces and with increased discharge frequencies.