Biology subjects

Kelly, L. A.

Publications and source records attributed to Kelly, L. A..

6 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↗

bioRxiv2024

Mitigating Stress: Exploring how our feet change shape with size

If human skeletal shape increases proportionally with size (isometric scaling) this can produce exponential increases in joint contact stresses. However, if skeletal shape changes as a function of size (allometric scaling) this can mitigate increases in joint contact stress by changing the surface area to volume ratio. Here we explored whether human foot bones scale with allometry and, if so, to identify the shape features that are associated with bone size. Computed tomography scans of the two largest foot bones (talus, calcaneus) were obtained from 36 healthy individuals. We implemented a scaling analysis for each joint surface area and bone. We performed a Procrustes ANOVA to establish the shape features associated with bone size. In line with our hypothesis, articular surfaces on the talus and the posterior facet of the calcaneus all scaled with positive allometry. Interestingly, the calcaneus scaled with negative allometry, appearing more cube-like with increasing size. This may be important for mitigation of internal bone stresses with increasing skeletal size. Our findings suggest distinct, but varied scaling strategies within the foot. This may reflect the requirement to maintain healthy joint contact and internal bone stresses with increasing size.

evolutionary biology↗

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↗

bioRxiv2022

Foot form and function: Variable and versatile, yet sufficiently related to predict one from the other

The modern human foot is a complex structure thought to play an important role in our ability to walk and run efficiently. Comparisons of our feet to those of our evolutionary ancestors and closest living relatives have linked the shape of several foot components (e.g., the longitudinal and transverse arches, size of the heel and length of the toes) to specific mechanical functions. But since foot shape varies widely across the modern human population, this study aimed to investigate how closely foot shape, deformation and joint mechanics during various locomotor tasks are actually linked. And whether the latter can be accurately predicted based entirely on the former two. A statistical shape-function model (SFM) was constructed by performing a principal component analysis on 100 participants three-dimensional foot scans, and joint angles and moments captured during level, uphill, and downhill walking and running. This SFM revealed that the main sources of variation were the longitudinal and transverse arches, relative foot proportions and toe shape along with their associated joint mechanics. However, each of these only accounted for a small proportion of the overall variation in foot shape, deformation and joint mechanics, most likely due to the high structural complexity and variability of the foot. Nevertheless, a leave-one-out analysis showed that the SFM can be used to accurately predict the joint angles and moments of a new foot based only on its shape. These results have implications and potential applicability across numerous fields, such as evolutionary anthropology, podiatry, orthopaedics and footwear design.

zoology↗

bioRxiv2022

Mobility of the human foot's medial arch enables upright bipedal locomotion

Developing the ability to habitually walk and run upright on two feet is one of the most significant transformations to have occurred in human evolution. Many musculoskeletal adaptations enabled bipedal locomotion, including dramatic structural changes to the foot and, in particular, the evolution of an elevated medial arch (H. Elftman and Manter, 1935). The foots arched structure has previously been assumed to play a central role in directly propelling the centre of mass forward and upward through leverage about the toes (Herbert Elftman and Manter, 1935) and a spring-like energy recoil (Hicks, 1955). Paradoxically, these roles seemingly require either arch rigidity (for the former) or mobility (for the latter). However, it is unclear whether or how the mobility and height of the medial arch support its propulsive lever function. Here we show, using high-speed biplanar x-ray, that regardless of intraspecific differences in medial arch height, arch recoil enables a longer contact time and favourable propulsive conditions for walking upright on an extended leg. This mechanism presumably helped drive the evolution of the longitudinal arch after our last common ancestor with chimpanzees, who lack this mobility during push-off. We discovered that the previously overlooked navicular-medial cuneiform joint is primarily responsible for this mobility in human arches, suggesting that future morphological investigations of this joint will provide new interpretations of the fossil record. Our work further suggests that enabling the mobility of the longitudinal arch in footwear and surgical interventions is critical for maintaining the ankles natural propulsive ability.

physiology↗

bioRxiv2019

Predicting spread and effective control measures for African swine fever - should we blame the boars?

African swine fever (ASF) has been causing multiple outbreaks in Russia, Poland and the Baltic countries in recent years and is currently spreading westwards throughout Europe and eastwards into China, with cases occurring in wild boar and domestic pigs. Curtailing further spread of ASF requires full understanding of the transmission pathways of the disease. Wild boars have been implicated as a potential reservoir for the disease and one of the main modes of transmission within Europe. We developed a spatially explicit model to estimate the risk of infection with ASF in boar and pigs due to the natural movement of wild boar that is applicable across the whole of Europe. We demonstrate the model by using it to predict the probability that early cases of ASF in Poland were caused by wild boar dispersion. The risk of infection in 2015 is computed due to wild boar cases in Poland in 2014, compared against the reported cases in 2015 and then the procedure is repeated for 2015-2016. We find that long- and medium-distance spread of ASF (i.e. >30km) is very unlikely to have occurred due to boar dispersal, due in part to the generally short distances boar will travel (<20km on average). We also predict what the relative success of different control strategies would have been in 2015, if they were implemented in 2014. Results suggest that hunting of boar reduces the number of new cases, but a larger region is at risk of ASF compared to no control measure. Alternatively, introducing boar-proof fencing reduces the size of the region at risk in 2015, but not the total number of cases. Overall, our model suggests wild boar movement is only responsible for local transmission of disease, thus other pathways are more dominant in medium and long distance spread of the disease.

epidemiology↗