Similar Running Speeds Research Articles

Inter-strides variability affects internal foot tissue loadings during running

Running overuse injuries result from an imbalance between repetitive loadings on the anatomical structures and their ability to adapt to these loadings. Unfortunately, the measure of these in-vivo loadings is not easily accessible. An optimal amount of movement variability is thought to decrease the running overuse injury risk, but the influence of movement variability on local tissue loading is still not known. A 3D dynamic finite element foot model driven by extrinsic muscle forces was developed to estimate the stress undergone by the different internal foot structures during the stance phase. The boundary conditions of different trials with similar running speed were used as input. Variability in bone stress (10%) and cartilage pressure (16%) can be expected while keeping the overall running speed constant. Bone and cartilage stress were mainly influenced by the muscle force profiles rather than by ground reaction force. These findings suggest, first, that the analysis of a single trial only is not representative of the internal tissue loadings distribution in the foot and second, that muscle forces must be considered when estimating bone and cartilage loadings at the foot level. This model could be applied to an optimal clinical management of the overuse injury.

High-intensity downhill running exacerbates heart rate and muscular fatigue in trail runners

ABSTRACT This study explores the cardiorespiratory and muscular fatigue responses to downhill (DR) vs uphill running (UR) at similar running speed or similar oxygen uptake (⩒O2). Eight well-trained, male, trail runners completed a maximal level incremental test and three 15-min treadmill running trials at ±15% slope: i) DR at ~6 km·h−1 and ~19% ⩒O2max (LDR); ii) UR at ~6 km·h−1 and ~70% ⩒O2max (HUR); iii) DR at ~19 km·h−1 and ~70% ⩒O2max (HDR). Cardiorespiratory responses and spatiotemporal gait parameters were measured continuously. Maximal isometric torque was assessed before and after each trial for hip and knee extensors and plantar flexor muscles. At similar speed (~6 km·h−1), cardiorespiratory responses were attenuated in LDR vs HUR with altered running kinematics (all p < 0.05). At similar ⩒O2 (~3 l·min−1), heart rate, pulmonary ventilation and breathing frequency were exacerbated in HDR vs HUR (p < 0.01), with reduced torque in knee (−15%) and hip (−11%) extensors and altered spatiotemporal gait parameters (all p < 0.01). Despite submaximal metabolic intensity (70% ⩒O2max), heart rate and respiratory frequency reached maximal values in HDR. These results further our understanding of the particular cardiorespiratory and muscular fatigue responses to DR and provide the bases for future DR training programs for trail runners.

Post‐emergence handling of green turtle hatchlings: improving hatchery management worldwide

AbstractHatcheries are commonly used to protect sea turtle eggs from poaching and predation; however, there is currently limited scientific evidence to support good hatchery management practices, particularly post‐hatching. This study investigated the effects of retaining hatchlings in hatcheries after emergence and delaying nest excavations on the quality of green turtle Chelonia mydas hatchlings. In addition, the effect of artificial lighting on the sea‐finding ability of green turtles was investigated to highlight the importance of hatchling release locations on hatchery beaches. Hatchling running speed, an indicator of vigour and predation exposure, progressively decreased when hatchlings were retained in the hatchery for 1, 3 and 6 hours following emergence. Similarly, body condition (mass : straight carapace length), an indicator of dehydration and/or energy consumption, decreased after being retained for 3 and 6 hours. It was estimated that hatchlings retained for 6 hours after emergence would become significantly dehydrated and double their exposure to beach slope predation. Residual hatchlings that were immediately excavated from emerged nests had similar running speed and body condition to naturally emerged siblings. However, residual hatchlings removed from nests 5 days later had significantly reduced running speed and body condition, resulting in estimates of double the exposure to predation in near‐shore areas. The mean angle of hatchling dispersal varied at different sites along the Ma’Daerah beach in relation to proximity to artificial lighting. Important recommendations for post‐hatching management of sea turtle hatcheries worldwide can be made from the results of this study. To maximize release of hatchlings in the best condition as is possible, hatchlings should be released immediately after emergence, including excavation of any residual hatchlings. In addition, the dispersal angles of hatchlings should be tested at each hatchery beach to determine suitable release sites for efficient dispersal.

Characteristics and classification of hippocampal theta rhythm induced by passive translational displacement

Theta rhythms in the hippocampus are believed to be the “metric” relating to various behavior patterns for free roaming rats. In this study, the theta rhythms were studied while rats either walked or were passively translated by a toy car on a linear track (referred to as WALK and TRANS respectively). For the similar running speeds in WALK and TRANS conditions, theta frequency and amplitude were both reduced during TRANS. Theta modulation of pyramidal cells during TRANS was reduced compared to that during WALK. Theta frequency was positively correlated with translation speed during TRANS. Theta rhythm remained apparent during TRANS and WALK after large dose of atropine sulfate (blocking the cholinergic pathway) was injected compared to still states. The present study demonstrated the patterns of theta rhythm induced by passive translation in rats and suggested that the Type I theta rhythm could occur during non-voluntary locomotion. We further argued that the perception of actual self-motion may be the underlying mechanism that initiates and modulates type I theta.

Metabolic-Cost Comparison Between Submaximal Land and Aquatic Treadmill Exercise

Purpose: To evaluate the metabolic cost of varying aquatic treadmill (ATM) exercise speed and water-jet resistance and compare with land treadmill (TM) conditions at similar running speeds. Methods: 15 participants (7 men, 8 women, age 22 + 4 years, height 173 + 8 cm, weight 66.9 + 9 kg) submerged to the xiphoid process completed nine 5-min submaximal ATM trials at 174-, 201-, and 228-m/min treadmill speeds with water-jet resistances set at 0%, 50%, and 75% of capacity. Oxygen consumption (VO2), expired ventilation (VE[BTPS]), tidal volume (VT), breath frequency (f), heart rate (HR), oxygen (O2), pulse, and ratings of perceived exertion (RPE) were recorded during each trial. The corresponding TM speeds that yielded VO2 costs similar to ATM conditions were determined. Repeated measures ANOVA and paired t tests were employed to determine significance (p < .05). Results: Increasing running speed and water-jet resistance both significantly increased VO2, HR, VE, (VE[BTPS]), pulse, and RPE. Women were lower (p < .05) than men in VO2, (VE[BTPS]), O2, pulse, and VT, and higher in HR and f in all ATM trials. Comparable (p < .05) metabolic costs (VO2) were observed when TM speeds were similar to ATM speeds without jet resistance. The addition of jet resistance increased (p < .01) the land TM required to elicit a similar metabolic costs by 27.8 and 54.6 m/min, respectively. Conclusions: These results suggest ATM yields similar metabolic costs to land TM in running speeds of 174-228 m/min.

Effects of hatchery shading and nest depth on the development and quality of Chelonia mydas hatchlings: implications for hatchery management in Peninsular, Malaysia

One of the decisions made by hatchery managers around the world is what degree of shading and nest depth are required to maximise the production of high-quality hatchlings at optimal sex ratios. The primary objectives of this study were to determine the effects of (1) hatchery shading and nest depth on nest temperatures and emergence lag, and (2) nest temperatures and nest depth on hatchling sex ratio and quality. In 2001, 26 Chelonia mydas clutches from Ma’Daerah beach, Terengganu, Malaysia, were relocated alternatively at depths of 50 cm and 75 cm into a 70%-shaded and a 100%-shaded hatchery. Data loggers were placed into the centre of each relocated clutch to record the temperature every hour over the course of incubation. When the hatchlings emerged, a sample of the clutch was run, measured and weighed and a separate sample was examined histologically for sex characteristics. Nest temperatures ranged between 28°C and 30°C and generally showed increases over the second half of incubation due to metabolic heating of the clutch. There was no significant correlation found between nest temperature and any of the hatchling parameters measured. Hatchlings from 75-cm-deep nests had a longer emergence lag (46.4 (±10.2) h) than hatchlings from 50-cm-deep nests. Hatch and emergence success were similar to those of natural populations and hatchling sex ratios were male dominant, with an average of 72% males. There was a poor correlation between mean middle-third incubation temperatures and sex ratio. Hatchlings from 75-cm-deep nests had similar running speeds but lower condition index than their conspecifics from 50-cm-deep nests.

Blood pH and lactate kinetics in the assessment of running endurance.

To study how two types of testing protocols for the determination of the [LA] and blood pH kinetics during running match each other, a group of nine runners participated in two testing protocols. The first protocol consisted of a sequences of 8 x 2000 m runs at constant speed, which was increased on different testing days. The first protocol was used for the determination of running speed (v), [LA], pH and heart rate (HR) corresponding to the Lactate Threshold (LT) and the Threshold of Acidosis (TA), both occurring at similar running speeds (4.21 +/- 0.44 and 4.22 +/- 0.40 m/s) (mean +/- SD) and HR (159 +/- 7 and 160 +/- 9 1/min), [LA] = 2.0 +/- 0.6 mmol/l and pH = 7.411 +/- 0.018. Maximal steady values for [LA] (maxLAss) and minimal steady values for pH (minpHss) obtained by the second protocol were higher (p < 0.01) according to running speed (4.62 +/- 0.38 and 4.66 +/- 0.38 m/s), HR (172 +/- 7 and 174 +/- 8 1/min) and [LA] (5.7 +/- 1.3 mmol/l) and lower according to pH (7.364 +/- 0.021), respectively. Unlike similar running speeds determined by LT and TA, the minimal steady pH level occurred at a slightly higher speed than the speed at maxLAss. Additionally, we found a drift of pH towards a resting level, when [LA] fluctuated around a steady level. Furthermore, the parameters of pH kinetics correlated better with the running speed of the 4000 m run that was taken as the parameter of short endurance performance, than those of [LA] kinetics. We conclude that these differences in [LA] and pH kinetics could serve to predict the capabilities of runners with respect to the two endurance performance types: long and short.

Stride Frequency and Submaximal Treadmill Running Economy in Adults and Children.

Previous studies have consistently shown that the body mass/relative oxygen cost of submaximal treadmill running is greater in children than in young adults. It has been suggested that the obligatory increased stride frequency in children might be at least partly responsible. This hypothesis was investigated by examining the association between stride frequency and oxygen demand characteristics in 10 aerobically fit prepubescent boys (ages 9-10 yrs) and 10 fit young men (ages 18-25 yrs) while running at fixed submaximal speeds on an electronically driven treadmill. The oxygen demand was higher at all running speeds in the boys' group. To compensate for a shorter stride length, the boys demonstrated higher stride frequency at all speeds. To determine if the inferior running economy in the boys was partly due to the greater stride frequency, the relative oxygen demand per stride was compared between groups at all speeds. This value was similar in both groups. It is concluded that the apparently greater oxygen demand of running in boys may be due in part to the greater stride frequency required to maintain similar running speeds.