The physiological cost of negative work

Abbott, B. C.; Bigland, Brenda; Ritchie, J. M.

doi:10.1113/jphysiol.1952.sp004755

Cited by 526 publications

(286 citation statements)

References 7 publications

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“…Similar findings have also been observed in eccentric cycling where, for the same metabolic cost, up to three times greater power can be produced compared to concentric cycling [5,12]. Furthermore the electrical activity (detectable with surface electromyography) at any given power or force production is less during eccentric compared to concentric exercise [3,6].…”

Section: Introductionsupporting

confidence: 71%

Familiarisation to maximal recumbent eccentric cycling

Green

Thomas

Ross

et al. 2017

IES

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Abstract. BACKGROUND:Isokinetic eccentric cycling is increasingly being utilised to examine the effect of chronic eccentric muscle training however little is known about how individuals familiarise to such a unique training modality. OBJECTIVE: To examine longitudinal variation in power output and lower limb muscle activation during familiarisation to maximal recumbent isokinetic eccentric cycling. METHODS: Twelve male volunteers, unfamiliar with eccentric cycling, completed four trials, separated by 7-10 days, each comprising 6 × 10 s maximal isokinetic eccentric efforts between 20-120 rpm. Peak power and average power output (PO), and surface electromyography (sEMG) of the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and medial gastrocnemius (MG) were recorded throughout. Systematic error across repeated trials was assessed using one-way ANOVA, and random error quantified using coefficient of variation (CV, %). RESULTS: Average PO at 60 rpm and RF activation at 20 rpm increased from trial 1-2 (p < 0.05), with no other systematic error between trials at any cadence. Across all cadences, the CV for peak PO (∼13%), average PO (∼10%), VL activation (∼13%) and RF activation (∼19%) was moderate and plateaued after one familiarisation (i.e. T2-T3). However, for BF (∼24%) and MG (∼22%) activation reliability was generally poor. For the majority of variables the reliability was best at 60 rpm. CONCLUSIONS: Therefore, with one familiarisation, 60 rpm is recommended to achieve moderate between-session reliability in the measurement of power output and lower limb muscle activation during recumbent, eccentric cycling.

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Section: Introductionsupporting

confidence: 71%

Familiarisation to maximal recumbent eccentric cycling

Green

Thomas

Ross

et al. 2017

IES

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“…This cancellation, however, does not affect the actual work exerted by a bat to flap its wings. The contribution of negative work to the overall inertial cost of flight should be no more than 20 per cent of the total, because muscle is roughly four times more efficient at performing negative work than positive work [16]. We therefore compute the inertial work by integrating the positive instantaneous power exerted over the course of the wingbeat cycle.…”

Section: Methodsmentioning

confidence: 99%

Upstroke wing flexion and the inertial cost of bat flight

et al. 2012

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Flying vertebrates change the shapes of their wings during the upstroke, thereby decreasing wing surface area and bringing the wings closer to the body than during downstroke. These, and other wing deformations, might reduce the inertial cost of the upstroke compared with what it would be if the wings remained fully extended. However, wing deformations themselves entail energetic costs that could exceed any inertial energy savings. Using a model that incorporates detailed three-dimensional wing kinematics, we estimated the inertial cost of flapping flight for six bat species spanning a 40-fold range of body masses. We estimate that folding and unfolding comprises roughly 44 per cent of the inertial cost, but that the total inertial cost is only approximately 65 per cent of what it would be if the wing remained extended and rigid throughout the wingbeat cycle. Folding and unfolding occurred mostly during the upstroke; hence, our model suggests inertial cost of the upstroke is not less than that of downstroke. The cost of accelerating the metacarpals and phalanges accounted for around 44 per cent of inertial costs, although those elements constitute only 12 per cent of wing weight. This highlights the energetic benefit afforded to bats by the decreased mineralization of the distal wing bones.

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“…Durante o exercício físico e comparativamente ao repouso, os músculos esqueléticos solicitados estão sujeitos a um maior stress metabólico e/ ou mecânico, dependendo do tipo de contrações efetuadas. As contrações excêntricas são aquelas com maior potencial lesivo para o músculo (20) , uma vez que, comparativamente às contrações concêntricas e isométricas, recrutam uma menor quantidade de unidades motoras para o mesmo trabalho efetuado, levando a uma distribuição do stress mecânico por uma menor quantidade de fibras musculares (1) . Desta forma, a prática inabitual ou extenuante de exercícios com predomínio de contrações excêntricas, pela grande sobrecarga mecânica imposta, tende a induzir dano sobre as estruturas musculares, podendo, em situações de grande exigência, motivar o aparecimento de uma entidade anatomopatológica nos músculos recrutados denominada por miopatia do exercício, com manifestações clínicas e laboratoriais (9) .…”

Section: Introductionunclassified

O treino com exercícios de contração excêntrica induz a longo prazo fibrose muscular esquelética

Pacheco¹,

Rocha²,

Teixeira³

et al. 2016

RPCD

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Músculo Quadriceps. RESUMOO exercício excêntrico (ExEx), inabitual ou extenuante, é um indutor de dano muscular esquelético. Contudo, quando repetido no tempo, de forma habitual, motiva tolerância muscular a essa agressão. Apesar das adaptações crónicas das fibras musculares poderem explicar alguma desta tolerância, não é de excluir a possível contribuição do aumento do tecido conjuntivo muscular para essa proteção induzida pelo treino. Assim, o objetivo deste trabalho foi o de avaliar as alterações no conteúdo de colagénio do músculo quadríceps sujeito a treino com ExEx. Ratos Wistar machos foram divididos em dois grupos (n = 5 por grupo): sedentário controlo (SED) e treinado (TR). Os animais TR praticaram corrida em tapete rolante (-25º; 30m/ minuto; 60 min) 1x/ semana, durante 8 semanas. A atividade sanguínea da creatina quinase (CK) foi avaliada ao longo do protocolo e, após sacrifício, recolheu-se o músculo quadríceps para análise histológica. Os resultados da CK demostraram o efeito protetor do treino ao exercício (p = .002). Nos músculos esqueléticos, observou-se um aumento da área de secção transversal (p < .000) das fibras musculares, simultaneamente com um aumento do conteúdo total de colagénio e da espessura do endomísio (p < .000). É possível concluir-se que, paralelamente ao efeito de tolerância, o treino ExEx promoveu um acentuado aumento do conteúdo muscular esquelético de colagénio e um incremento moderado da área de secção transversal das fibras musculares. there was a moderate increase in muscle fibbers cross-sectional area (p < 0.000), simultaneously with a huge increase in the total collagen content and endomysium thickness (p < .000). It can be concluded that, in addition to the tolerance effect, EcEx training induced a remarkable increase in skeletal muscle collagen content, in parallel with a moderate increase of muscle fibbers' cross-sectional area.

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The physiological cost of negative work

Cited by 526 publications

References 7 publications

Familiarisation to maximal recumbent eccentric cycling

Familiarisation to maximal recumbent eccentric cycling

Upstroke wing flexion and the inertial cost of bat flight

O treino com exercícios de contração excêntrica induz a longo prazo fibrose muscular esquelética

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