External load can alter the energy cost of prolonged exercise

Epstein, Yoram; Rosenblum, Joseph; Burstein, R.; Sawka, Michael N.

doi:10.1007/bf00640670

Cited by 73 publications

(44 citation statements)

References 19 publications

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“…One study of 6 trained subjects who were asked to walk on a treadmill with 25-and 40-kg backpacks found that heavier loads resulted in increased energy costs over time. 19 Similarly, the exercise intolerance of overweight adolescents that we observed could be attributed to increased energy demands as a result of the extra load from excess adiposity. Our study demonstrated that the negative correlation between D12 and BMI was a continuous phenomenon: the greater the BMI, the more severe the functional impairment.…”

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confidence: 51%

“…These studies have concluded that exercise intolerance in overweight children and adolescents is attributable primarily to the increased metabolic demands of carrying an excess load, rather than a true decrease in cardiorespi-ratory fitness. 15,[18][19][20] However, some studies have reported that overweight individuals have significantly decreased maximal heart rate; heart rate reserve, which is defined as maximal heart rate minus resting heart rate 15,16,21 ; and myocardial work efficiency. 22 Whether these differences significantly influence fitness and performance is unclear.…”

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Influence of Excess Adiposity on Exercise Fitness and Performance in Overweight Children and Adolescents

et al. 2005

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ABSTRACT. Objective. Relatively little is known about how excess body mass affects adolescents' capacity to perform sustained exercise. We hypothesized that most of the difficulty that severely overweight adolescents have with sustained exercise occurs because the metabolic costs of moving excess mass result in use of a high proportion of their total oxygen reserve.Methods. We compared results from a maximal cycle ergometry fitness test in 129 severely overweight adolescents who had BMIs of 41.5 ؎ 9.7 kg/m 2 and ages of 14.5 ؎ 1.8 years (range: 12.1-17.8 years) and 34 nonoverweight adolescents who had BMIs of 20.1 ؎ 2.9 kg/m 2 and ages of 14.5 ؎ 1.5 years (range: 12.0 -18.1 years). Oxygen uptake (V O 2 ) was compared at 3 times: during a 4-minute period of unloaded cycling (ULV O 2 ), at the lactate threshold estimated by gas exchange (LTV O 2 ), and at maximal exertion (V O 2 max). Heart rate was obtained at rest and at V O 2 max. Participants also completed a 12-minute walk/ run performance test to obtain distance traveled (D12) and heart rate. Results. Absolute LTV O 2 and V O 2 max and LTV O 2 as a percentage of V O 2 max were not different in overweight and nonoverweight adolescents during the cycle test.However, absolute ULV O 2 was significantly greater in overweight adolescents: ULV O 2 accounted for 35 ؎ 8% of V O 2 max (and 63 ؎ 15% of LTV O 2 ) in overweight adolescents but only 20 ؎ 5% of V O 2 max (and 39 ؎ 12% of LTV O 2 ) in nonoverweight adolescents. Resting heart rate before initiating the cycle test was significantly greater in overweight than nonoverweight adolescents (94 ؎ 14 vs 82 ؎ 15 beats per minute). However, maximal heart rate during the cycle test was significantly lower in overweight adolescents (186 ؎ 13 vs 196 ؎ 11 beats per minute). During the walk/run test, mean D12 was significantly shorter for overweight than for nonoverweight adolescents (1983 ؎ 323 vs 1159 ؎ 194 m). D12 was negatively related to BMI SDS (r ‫؍‬ ؊0.81) and to ULV O 2 (r ‫؍‬ ؊0.98).Discussion. Overweight and nonoverweight adolescents had similar absolute V O 2 at the lactate threshold and at maximal exertion, suggesting that overweight adolescents are more limited by the increased cardiorespiratory effort required to move their larger body mass through space than by cardiorespiratory deconditioning. ABBREVIATIONS. V o 2 max, maximum oxygen uptake; SDS, SD score; ULV o 2 , unloaded oxygen uptake; LTV o 2 , oxygen uptake at the lactate threshold; V o 2 max, oxygen uptake at maximal exertion; HRR, heart rate reserve; RPE, rating of perceived exertion; bpm, beats per minute; D12, distance achieved at 12 minutes during walk/run test; ANCOVA, analysis of covariance. O verweight during childhood has been identified as a major health problem in the United States. 1-4 Pediatric overweight commonly presages adult obesity 5 and is associated with the development of weight-related comorbid conditions and increased morbidity. [6][7][8] Decreased physical activity and a more sedentary lifestyle have been implicated as importan...

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Influence of Excess Adiposity on Exercise Fitness and Performance in Overweight Children and Adolescents

et al. 2005

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“…In general, those changes have been shown to contribute to, or are at least suggestive of, an elevated energy cost of movement, an earlier onset of fatigue, and possibly an increased risk of injury (Epstein et al 1988;Knapik et al 2004). Morever, during deliberate mass placements away from the midline, those outcomes also show a lateral dependency, with an even greater postural disturbance and more rapid fatigue development (Park et al 2014).…”

Section: Load Carriage and Its Impact Upon Gaitmentioning

confidence: 99%

Load carriage, human performance, and employment standards

Taylor

Peoples

Petersen

2016

Appl. Physiol. Nutr. Metab.

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Abstract:The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20-25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.Key words: backpacks, firefighter, load carriage, oxygen cost, military, employment standards, ventilation, work of breathing.Résumé : Cette analyse documentaire traite principalement des aspects physiologiques essentiels à l'élaboration de normes d'emploi pour des postes dont la fonction majeure est le transport de charges. Les employés dans l'armée, les pompiers, la police, les membres de recherche et sauvetage travaillent régulièrement avec de lourdes charges. Par exemple, les soldats transportent souvent des charges de >50 kg et les pompiers de bâtiments portent un vêtement de protection pesant de 20 à 25 kg et déplacent aussi des charges externes. On sait depuis longtemps que le port de charges lourdes modifie la démarche, la mobilité, le taux métabolique et le rendement tout en augmentant le risque de fatigue musculaire et de blessure. De plus, le déplacement des charges est effectué fréquemment dans des conditions environnementales stressantes et les vêtements de protection accroissent la charge thermique dans cet endroit. En outre, la contrainte physiologique ne dépend pas seulement de la masse et des dimensions des objets à déplacer, mais aussi de leur positionnement sur et autour du corps. Pourtant, il faut que ces charges soient déplacées par des hommes et des femmes de gabarit divers dont les capacités opérationnell...

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“…When subjects perform a loaded road march on a treadmill at a constant speed, exercise intensity increases over time if the load or speed is high enough (16,41). However, in the present study there was little change in exercise intensity (heart rate) in spite of large changes in march speed (Table 9) and environmental temperature.…”

Section: Performance Testsmentioning

confidence: 99%