Performance determinants, running energetics and spatiotemporal gait parameters during a treadmill ultramarathon.

PURPOSE: The objective of this study was to investigate the changes in metabolic variables, running energetics and spatiotemporal gait parameters during an 80.5 km treadmill ultramarathon and establish which key predictive variables best determine ultramarathon performance. METHODS: Twelve participants (9 male and 3 female, age 34 ± 7 years, and maximal oxygen uptake ([Formula: see text]O2max) 60.4 ± 5.8 ml·kg-1·min-1) completed an 80.5 km time trial on a motorised treadmill in the fastest possible time. Metabolic variables: oxygen consumption ([Formula: see text]O2), carbon dioxide production ([Formula: see text]CO2) and pulmonary ventilation ([Formula: see text]E) were measured via indirect calorimetry every 16.1 km at a controlled speed of 8 km·h-1 and used to calculate respiratory exchange ratio (RER), the energy cost of running (Cr) and fractional utilisation of [Formula: see text]O2max (F). Spatiotemporal gait parameters: stride length (SL) and cadence (SPM) were calculated via tri-axial accelerometery. RESULTS: Trial completion time was 09:00:18 ± 01:14:07 (hh:mm:ss). There were significant increases in [Formula: see text]O2, Cr, F, [Formula: see text]E and heart rate (HR) (p < 0.01); a significant decrease in RER (p < 0.01) and no change in SL and SPM (p > 0.05) across the measured timepoints. F and Cr accounted for 61% of the variance in elapsed finish time ([Formula: see text] = 0.607, p < 0.01). CONCLUSION: A treadmill ultramarathon elicits significant changes in metabolic variables, running energetics and spatiotemporal gait parameters. With F and Cr explaining 61% of variance in finish time. Therefore, those able to maintain a higher F, while adopting strategies to minimise an increase in Cr may be best placed to maximise ultramarathon performance.

Ontogenetic scaling of pelvic limb muscles, tendons and locomotor economy in the ostrich (Struthio camelus).

In rapidly growing animals there are numerous selective pressures and developmental constraints underpinning the ontogenetic development of muscle-tendon morphology and mechanical properties. Muscle force generating capacity, tendon stiffness, elastic energy storage capacity and efficiency were calculated from muscle and tendon morphological parameters and in vitro tendon mechanical properties obtained from a growth series of ostrich cadavers. Ontogenetic scaling relationships were established using reduced major axis regression analysis. Ostrich pelvic limb muscle mass and cross-sectional area broadly scaled with positive allometry, indicating maintained or relatively greater capacity for maximum isometric force generation in larger animals. The length of distal limb tendons was found to scale with positive allometry in several tendons associated with antigravity support and elastic energy storage during locomotion. Distal limb tendon stiffness scaled with negative allometry with respect to body mass, with tendons being relatively more compliant in larger birds. Tendon material properties also appeared to be size-dependent, suggesting that the relative increased compliance of tendons in larger ostriches is due in part to compensatory distortions in tendon material properties during maturation and development, not simply from ontogenetic changes in tendon geometry. Our results suggest that the previously reported increase in locomotor economy through ontogeny in the ostrich is due to greater potential for elastic energy storage with increasing body size. In fact, the rate of this increase may be somewhat greater than the conservative predictions of previous studies, thus illustrating the biological importance of elastic tendon structures in adult ostriches.

An isokinetic method for inducing a localised fatigue effect in the plantarflexors and dorsiflexors of the ankle.

To examine the effects of dysfunction of specific musculature of the shank a reliable and valid protocol can be used to induce a localised fatigue effect. A localised dynamometry based protocol was developed to illicit a fatigue effect in either plantar flexors or dorsiflexors. An isokinetic protocol allowing for movement through the full range of motion, set at an angular velocity of 45°s(-1), was used to allow fatigue to be developed. Fatigue was established when three consecutive torque measures dropped below 50% of the average three peak contractions. Bouts of activity were based on a ratio of 40 contractions interspaced with a 30s rest. Results suggest that the protocol elicited a fatigue effect in the prime movers of either plantar flexion or dorsiflexion, supported through the analysis of power spectral density and amplitude shift of surface electromyography measures. The protocol demonstrated sound reliability with Interclass Correlation scores for all measures ranging from 0.441-0.962. The protocol is a valid and repeatable process for establishing muscular weakness in the working muscles of either plantar or dorsi flexion, as observed in the fatigued state. This can allow further examination of the effects of a localised muscular weakness on daily living tasks.