Update and extension of the 'equivalent slope' of speed-changing level locomotion in humans : a computational model for shuttle running

Controlled experimental protocols for metabolic cost assessment of speed-changing locomotion are quite complex to design and manage. The use of the 'equivalent slope', i.e. the gradient locomotion at constant speed metabolically equivalent to a level progression in acceleration, has proved valuable in the estimation of the metabolic cost of speed-changing gaits. However, its use with steep slopes requires extrapolation of the experimental cost versus gradient function for constant running speed, resulting in less-reliable estimates. The present study extended the model to also work with deceleration, and revised the predictive equation to enable it to be applied to much higher levels of speed change. Shuttle running at different distances (from 5+5 to 20+20\u2005m) was then investigated using the novel approach and software, and the predictions in terms of metabolic cost and efficiency compare well with the experimental data

ASPECTS OF THE ENERGETICS AND THE MECHANICS OF HUMAN LOCOMOTION

The relationship between the mechanical work performed by the muscles during locomotion and the corresponding metabolic energy consumption is still not completely understood beside the methodological problems and the inherent assumptions in the calculation of both mechanical work and metabolic energy it seems that many factors can affect this relationship. They can be of very different nature depending on muscle structure and composition, body dimension. kinetic and kinematic parameters. The analysis of the mechanical work, in terms of its two component, external work !that done to lift and to accelerate the centre of mass at each step) and internal work (that of accelerating the limbs relative to the body centre of mass), together with the measurement of the metabolic energy consumption, appears a useful approach to better understand the determinants of many characteristics of human locomotion. The relevance of the external and of the internal work has been inferred by altering them separately in particular conditions as in uphill and downhill walking and running or in loaded locomotion (adding 'weight to the trunk or to the limbs).Optimization processes that seem to set the normal speed of walking of unrestrained subjects, the speed of spontaneous transition from walking to running. the frequency freely adopted at a given gait and speed seem better explained on these bases Yet, from the results so far obtained, it appears that neither mechanical work and energy cost are the sole determinants of many aspects of human locomotion

Pedaling rate is an important determinant of human oxygen uptake during exercise on the cycle ergometer.

Estimation of human oxygen uptake (V˙o2) during exercise is often used as an alternative when its direct measurement is not feasible. The American College of Sports Medicine (ACSM) suggests estimating human V˙o2 during exercise on a cycle ergometer through an equation that considers individual's body mass and external work rate, but not pedaling rate (PR). We hypothesized that including PR in the ACSM equation would improve its V˙o2 prediction accuracy. Ten healthy male participants' (age 19-48 years) were recruited and their steady-state V˙o2 was recorded on a cycle ergometer for 16 combinations of external work rates (0, 50, 100, and 150 W) and PR (50, 70, 90, and 110 revolutions per minute). V˙o2 was calculated by means of a new equation, and by the ACSM equation for comparison. Kinematic data were collected by means of an infrared 3-D motion analysis system in order to explore the mechanical determinants of V˙o2. Including PR in the ACSM equation improved the accuracy for prediction of sub-maximal V˙o2 during exercise (mean bias 1.9 vs. 3.3 mL O2 kg(-1) min(-1)) but it did not affect the accuracy for prediction of maximal V˙o2 (P > 0.05). Confirming the validity of this new equation, the results were replicated for data reported in the literature in 51 participants. We conclude that PR is an important determinant of human V˙o2 during cycling exercise, and it should be considered when predicting oxygen consumption

A "wearable" test for maximum aerobic power : real-time analysis of a 60-m sprint performance and heart rate off-kinetics

Maximum aerobic power (V.O2peak) as an indicator of body fitness is today a very well-known concept not just for athletes but also for the layman. Unfortunately, the accurate measurement of that variable has remained a complex and exhaustive laboratory procedure, which makes it inaccessible to many active people. In this paper we propose a quick estimate of it, mainly based on the heart rate off-kinetics immediately after an all-out 60-m sprint run. The design of this test took into account the recent availability of wrist wearable, heart band free, multi-sensor smart devices, which could also inertially detect the different phases of the sprint and check the distance run. 25 subjects undertook the 60-m test outdoor and a V.O2peak test on the laboratory treadmill. Running average speed, HR excursion during the sprint and the time constant (t) of HR exponential decay in the off-kinetics were fed into a multiple regression, with measured V.O2peak as the dependent variable. Statistics revealed that within the investigated range (25-55 ml O2/(kg min)), despite a tendency to overestimate low values and underestimate high values, the three predictors confidently estimate individual V.O2peak (R2= 0.65, p < 0.001). The same analysis has been performed on a 5-s averaged time course of the same measured HR off-kinetics, as these are the most time resolved data for HR provided by many modern smart watches. Results indicate that despite of the substantial reduction in sample size, predicted V.O2peak still explain 59% of the variability of the measured V.O2peak

Anatomically asymmetrical runners move more asymmetrically at the same metabolic cost.

We hypothesized that, as occurring in cars, body structural asymmetries could generate asymmetry in the kinematics/dynamics of locomotion, ending up in a higher metabolic cost of transport, i.e. more 'fuel' needed to travel a given distance. Previous studies found the asymmetries in horses' body negatively correlated with galloping performance. In this investigation, we analyzed anatomical differences between the left and right lower limbs as a whole by performing 3D cross-correlation of Magnetic Resonance Images of 19 male runners, clustered as Untrained Runners, Occasional Runners and Skilled Runners. Running kinematics of their body centre of mass were obtained from the body segments coordinates measured by a 3D motion capture system at incremental running velocities on a treadmill. A recent mathematical procedure quantified the asymmetry of the body centre of mass trajectory between the left and right steps. During the same sessions, runners' metabolic consumption was measured and the cost of transport was calculated. No correlations were found between anatomical/kinematic variables and the metabolic cost of transport, regardless of the training experience. However, anatomical symmetry significant correlated to the kinematic symmetry, and the most trained subjects showed the highest level of kinematic symmetry during running. Results suggest that despite the significant effects of anatomical asymmetry on kinematics, either those changes are too small to affect economy or some plastic compensation in the locomotor system mitigates the hypothesized change in energy expenditure of running

Movement in low gravity environments (MoLo) programme The Molo-L.O.O.P. study protocol

The aim of this paper is to define an experimental protocol and methodology suitable to estimate in high-fidelity hypogravity conditions the lower limb internal joint reaction forces. State-of-the-art movement kinetics, kinematics, muscle activation and muscle-tendon unit behaviour during locomotor and plyometric movements will be collected and used as inputs (Objective 1), with musculoskeletal modelling and an optimisation framework used to estimate lower limb internal joint loading (Objective

Evaluation of presumably disease causing SCN1A variants in a cohort of common epilepsy syndromes

Objective: The SCN1A gene, coding for the voltage-gated Na+ channel alpha subunit NaV1.1, is the clinically most relevant epilepsy gene. With the advent of high-throughput next-generation sequencing, clinical laboratories are generating an ever-increasing catalogue of SCN1A variants. Variants are more likely to be classified as pathogenic if they have already been identified previously in a patient with epilepsy. Here, we critically re-evaluate the pathogenicity of this class of variants in a cohort of patients with common epilepsy syndromes and subsequently ask whether a significant fraction of benign variants have been misclassified as pathogenic. Methods: We screened a discovery cohort of 448 patients with a broad range of common genetic epilepsies and 734 controls for previously reported SCN1A mutations that were assumed to be disease causing. We re-evaluated the evidence for pathogenicity of the identified variants using in silico predictions, segregation, original reports, available functional data and assessment of allele frequencies in healthy individuals as well as in a follow up cohort of 777 patients. Results and Interpretation: We identified 8 known missense mutations, previously reported as path

The biomechanics of skipping gaits : a third locomotor paradigm?

Skipping, a gait children display when they are about four- to five-years-old, is revealed to be more than a behavioural peculiarity. By means of metabolic and biomechanical measurements at several speeds, the relevance of skipping is shown to extend from links between bipedal and quadrupedal locomotion (namely galloping) to understanding why it could be a gait of choice in low-gravity conditions, and to some aspects of locomotion evolution (ground reaction forces of skipping seem to originate from pushing the walking gait to unnaturally high speeds). When the time-courses of mechanical energy and the horizontal ground reaction force are considered, a different locomotion paradigm emerges, enabling us to separate, among the bouncing gaits, the trot from the gallop (quadrupeds) and running from skipping (bipeds). The simultaneous use of pendulum-like and elastic mechanisms in skipping gaits, as shown by the energy curve analysis, helps us to understand the low cost of transport of galloping quadrupeds

Contraction dynamics in antagonist muscles

By taking into account the torque/angle and the torque/angular speed relationships of antagonist muscles acting across a joint it is possible to predict the contraction dynamics when they are simultaneously activated at a constant level. The simulation is displayed in a "phase-plane" where trajectories for each starting condition (angle--abscissa, angular speed--ordinate) represent the contraction dynamics. The results vary in the position of attractors, repulsors and trajectory shapes. Attractor points (at zero speed) have particular significance in joint stabilization. It was found that with certain reciprocal torque/angle relationships of antagonist muscles, a range of stable joint angles can be quickly reached just by selecting the proper group activation level. A given ratio between the activation levels selects the stable joint angle (attractor) while the overall amplitude will set the joint stiffness in that position. Thus a hypothesized control system should choose just two neural activation amplitudes (time-course considerations are unnecessary), with a reduction of the information needed to stiffen the joint. Furthermore, even ignoring the effects of joint friction, the trajectories toward attractors showed a tendency to cross the zero speed boundary no more than once, resembling the behaviour of an overdamped spring-dashpot system. A couple of testing simulations demonstrated that the combination of non-linear torque/angle and torque/speed relationships is essential to avoid tremor-like paths about the equilibrium and to quickly stiffen the joint. Other aspects related to co-contractions are discussed in the paper