Biology subjects

Cresswell, A. G.

Publications and source records attributed to Cresswell, A. G..

3 recordsLinked to original sources

bioRxiv2024

Dissecting the metabolic costs of up- and down-hill walking

Work- and collision-based models of locomotion are often used to describe the relationship between the bodys mechanical work requirements and metabolic energy expenditure. While work- and collision-based models do a reasonable job of relating mechanical work to metabolic cost at a system level, these models may not map to the underlying force and work demands of muscle, which directly affects energy expenditure. We collected motion capture, force, electromyography and ultrasound data from the main power producing muscles during uphill and downhill walking between +/- 15% grade. These data were used to evaluate a musculoskeletal modelling approach to simulate muscle force- and work-related costs that could be compared to metabolic power that we measured using indirect calorimetry. Muscle force-related costs (activation heat rate + maintenance heat rate) increased at steeper up- and down-hill grades and were moderately correlated with mean joint moments. Muscle work-related costs (mechanical work rate + shortening / lengthening heat rate) increased as grade became more positive and were strongly correlated with net joint work. Compared to traditional models, the inclusion of a term to account for muscle force-related costs should lead to a more explanatory cost model that maps directly to the mechanical demands of muscle.

physiology↗

bioRxiv2023

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, lateral gastrocnemius (GL), soleus (SOL), tibialis anterior, vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF), and the work requirements GL, SOL and VL. Gross metabolic power increased with a decrease in hop frequency and increase in hop height. There was no hop frequency or hop height effect on the mean electromyography (EMG) of ankle musculature, however, the mean EMG of VL and RF increased with a decrease in hop frequency and that of BF increased with an increase in hop height. With a reduction in hop frequency, GL, SOL and VL fascicle shortening, fascicle shortening velocity and fascicle to MTU shortening ratio increased, whereas with an increase in hop height, only SOL fascicle shortening velocity increased. Therefore, within the constraints that we imposed, decreases in hop frequency and increases in hop height resulted in increases in metabolic power that could be explained by increases in the activation requirements of knee musculature and/or increases in the work requirements of both knee and ankle musculature. Summary StatementThis study directly measures activation and work requirements of lower-limb musculature and whole-body metabolic energy requirements across a wide variety of human hopping conditions, helping to guide biomechanical models of energy expenditure.

physiology↗

bioRxiv2021

Concurrent assessment of motor unit firing properties and fascicle length changes with high-density surface electromyography ultrasound-transparent electrodes

The integration of electromyography (EMG) and ultrasound imaging has provided important information about the mechanisms of muscle activation and contraction. Unfortunately, EMG does not allow an accurate assessment of the interplay between the neural drive received by muscles, changes in fascicle length (FL) and the force/torque produced. We aimed to assess the relationship between modulations in tibialis anterior (TA) motor unit (MU) firing rate, FL and dorsiflexion torque (DT) using ultrasound-transparent high-density EMG electrodes. EMG and ultrasound images were recorded simultaneously from TA, using a 32-electrode silicon matrix, while performing isometric dorsiflexion, at diverse ankle joint positions (0{degrees} and 30{degrees} plantar flexion) and torques (20% and 40% of maximum). EMG signals were decomposed into individual MUs and changes in FL were assessed with a fascicle-tracking algorithm. MU firings were converted into a cumulative spike train (CST) that was cross-correlated with DT (CST-DT) and FL (CST-FL). High cross-correlations were found for CST-FL, 0.60 (range: 0.31-0.85) and CST-DT 0.71 (range: 0.31-0.88). Cross-correlation lags revealed that the delay between CST-FL (~75ms) was significantly smaller than CST-DT (~150ms, p<0.001). These delays affected the interpretation of MU recruitment/de-recruitment thresholds, with FL showing similar lengths for both recruitment and de-recruitment. This study is the first to demonstrate that changes in TA FL are closely related to both modulations in MU firing frequency and DT. These relationships allow assessment of the interplay between neural drive, muscle contraction and resultant torque, thereby providing a better understanding of the mechanisms responsible for the generation of muscle force. NEW AND NOTEWORTHYBy employing ultrasound-transparent high-density surface EMG electrodes, we show that modulations in tibialis anterior motor unit discharge rate were closely related to both changes in its fascicle length and resultant torque. These relationships allowed quantifying delays between neural drive and muscle shortening as well as muscle shortening and torque during submaximal isometric contractions, providing an accurate estimation of the time required to generate muscle force and subsequent production of torque via the tendon.

physiology↗