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Copyright © This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. This study introduces a new method to understand how added load affects human performance across a broad range of athletic tasks (ten obstacles) embedded in an outdoor obstacle course. The method employs an array of wearable inertial measurement units (IMUs) to wirelessly record the movements of major body segments to derive obstacle-specific metrics of performance. The effects of load are demonstrated on (N = 22) participants who each complete the obstacle course under four conditions including unloaded (twice) and with loads of 15% and 30% of their body weight (a total of 88 trials across the group of participants). The IMU-derived performance metrics reveal marked degradations in performance with increasing load across eight of the ten obstacles. Overall, this study demonstrates the significant potential in using this wearable technology to evaluate human performance across multiple tasks and, simultaneously, the adverse effects of body-borne loads on performance. The study addresses a major need of military organizations worldwide that frequently employ standardized obstacle courses to understand how added loads influence warfighter performance. Importantly, the findings and conclusions drawn from IMU data would not be possible using traditional timing metrics used to evaluate task performance.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Running agility is required for many sports and other physical tasks that demand rapid changes in body direction. Quantifying agility skill remains a challenge because measuring rapid changes of direction and quantifying agility skill from those measurements are difficult to do in ways that replicate real task/game play situations. The objectives of this study were to define and to measure agility performance for a (five-cone) agility drill used within a military obstacle course using data harvested from two foot-mounted inertial measurement units (IMUs). Thirty-two recreational athletes ran an agility drill while wearing two IMUs secured to the tops of their athletic shoes. The recorded acceleration and angular rates yield estimates of the trajectories, velocities and accelerations of both feet as well as an estimate of the horizontal velocity of the body mass center. Four agility performance metrics were proposed and studied including: 1) agility drill time, 2) horizontal body speed, 3) foot trajectory turning radius, and 4) tangential body acceleration. Additionally, the average horizontal ground reaction during each footfall was estimated. We hypothesized that shorter agility drill performance time would be observed with small turning radii and large tangential acceleration ranges and body speeds. Kruskal-Wallis and mean rank post-hoc statistical analyses revealed that shorter agility drill performance times were observed with smaller turning radii and larger tangential acceleration ranges an d body speeds, as hypothesized. Moreover, measurements revealed the strategies that distinguish high versus low performers. Relative to low performers, high performers used sharper turns, larger changes in body speed (larger tangential accele

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. In vehicle dynamics, it is commonly understood that there is an inverse relationship between stability and maneuverability. However, animal studies have found that stability and maneuverability can coincide. In this study, we examine humans running a reactive agility obstacle and consider the relationship between observational perceived agility and balance, as well as the relationship between quantified surrogates of agility and balance. Recreational athletes (n = 18) completed the agility task while wearing inertial measurement units (IMUs) on their body. The task was also video-recorded. An observational study was completed by a separate group of adults (n = 33) that were asked to view the videos and score each athlete on a Likert scale for balance and for agility. The data from the body-worn IMUs were used to estimate quantified surrogate measures for agility and balance, and to assess if the relationship between the quantified agility and balance was in the same direction as the perceived relationship from the Likert scale responses. Results indicate that athletes that were given a higher Likert agility score were also given a higher balance score (rs= 0.75,p < 0.001). Quantitative surrogates of agility and balance also showed this same relationship. Additional insights on technique for this reactive agility task were informed by the quantitative surrogates. We observed the importance of stepping technique in achieving the faster completion times. The fast performing athletes spent a greater proportion of the task in double support and lower overall time in single support indicating increased periods of static stability. The fast performing athletes did not have a higher body speed, but performed the task with a more efficient tec

Heart rate, mean arterial pressure, respiratory rate, minute volume, arterial blood PO2, PCO2, pH, hemoglobin saturation, lactic acid, and pyruvic acid were determined on anesthetized dogs during progressive hyperthermia. Heart rate increased as rectal temperature (Tr) in creased. Mean arterial pressure began to decline at Tr between 41 and 42 C. Respiratory rate and minute volume reached maximum values at tempera tures around 42 C. Arterial PO2 and hemoglobin saturation did not decrease until rectal tempera ture exceeded 42 C. PCO2 decreased and pH in creased from control values as minute volume increased. Arterial excess lactate showed the most marked rise at Tr's between 41 and 42 C. The conclusion was made that failure of external respiration is not the primary physiologic failure during progressive hyperthermia but the development of tissue hypoxia may be. (Author)

The oxygen deficit incurred during hypoxia was compared to the peak excess lactate (XL) level in order to see if any consistent relationship existed when a known oxygen limitation was imposed. Twelve anesthetized dogs, in which ventilation was held constant, breathed 9.1% O2 in N2 for 10, 20, and 30 minutes. Oxygen uptake was measured every 10 minutes during a control period, hypoxia, and a recovery period. Oxygen content and tension of systemic and pulmonary arterial blood were measured at the end of each of these periods. Excess lactate was calculated from blood lactate and pyruvate levels measured during the control period, the last minute of hypoxia, the first minute of recovery, and at intervals thereafter. Depletion and repletion of oxygen stores were estimated by assuming values on a body-weight basis for functional residual volume, body water, total blood volume, and its distribution. 'True' O2 deficit and 'true' excess O2 of recovery were thus calculated and compared to each other and to peak XL values. Excess O2 uptake measured during recovery, which is the oxygen debt as usually measured, never was as great as the oxygen deficit incurred during hypoxia, and bore little consistent relationship to peak XL. The 'true' O2 deficit, on the other hand, had a coefficient of correlation of .781 when compared with peak XL.

Oxygen consumption, body temperature, plasma lactic acid and ketones were measured in male mongrel dogs, anesthetized, paralyzed, artificially ventilated and cooled in a water bath at 34C. Treatment included inspiration of 10 or 20% CO2, beta adrenergic blockade (propranolol), and beta blockade plus 10% CO2. All treatments resulted in a lower oxygen consumption than controls (P < .05) with the 20% CO2 group showing a greater depression than the other three experimental groups (P < .05). The rate of decline in body temperature was greater while breathing 20% CO2 than room air (P < .05). Beta adrenergic blockade resulted in a drop in lactate levels compared with controls (P < .05), while a further drop occurred with beta blockade plus 10% CO2 (P < .025). Plasma free fatty acids tended to decrease with propranolol or 10% CO2, but the only significant difference detected was an increased downtrend during the first 30 min with the combined treatment. It was concluded that the increased rate of decline of body temperature with hypercapnia was due to decreased heat production primarily by inhibition of the beta-adrenergic calorigenic processes., Pub. in Aerospace Medicine, v43 n3 p287-290 Mar 1972.

When anesthetized dogs were made hypoxic at constant ventilation, increases in arterial lactate (delta L) compared as well to net O2 deficit (NOD) as did excess lactate (XL). It was asked whether this would hold true if PCO2 was varied during hypoxia. Twelve dogs were made hypoxic for 30 minutes while eucapnic (PCO2 = 40 torr) and again while hypercapnic (PCO2 = 77 torr), with appropriate control and recovery periods. Another group of 12 dogs were treated similarly except one hypoxic period was hypocapnic (PCO2 = 18 torr) and the other eucapnic. NOD was estimated from the total decrease in VO2 during hypoxia by assuming that baseline VO2 would have been unchanged if PO2 was not limited, and by estimating the change in O2 stores during hypoxia. Net O2 repayment (NOR) was estimated similarly. In a graph of delta L against NOD, three different lines were obtained according to the PCO2 level. The same was true for XL against NOD. In 36 or 48 comparisons, NOR was less than NOD. Of the 12 comparisons in which NOR was larger, 7 were hypocapnic, 4 were eucapnic, and only 1 was hypercapnic. In addition to direct effects of altered intracellular pH on lactate metabolism, PCO2 may also alter baseline energy demand during hypoxia by its effect on calorigenesis of liberated catecholamines.