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Exp Physiol. 2019 Nov 27. doi: 10.1113/EP088087. [Epub ahead of print]

The effects of long-term muscle disuse on neuromuscular function in unilateral transtibial amputees.

Author information

1
Department of Life Sciences, University of Roehampton, London, UK.
2
Department of Allied Health Sciences, London South Bank University, London, UK.
3
Department of Family Medicine, University of North Texas Health Science Center, Fort Worth, Texas, USA.

Abstract

NEW FINDINGS:

What is the central question of this study? The effects of long-term muscle disuse on neuromuscular function are unclear because disuse studies are typically short-term. This study used a novel model (unilateral transtibial amputees) to investigate the effects of long-term disuse on quadriceps neuromuscular function. What is the main finding and its importance? Kinetic analysis (knee extension moments during gait) indicated habitual disuse of the amputated limb quadriceps, accompanied by lower quadriceps muscle strength (60-76%) and neural activation (32-44%), slower contractile properties, and altered muscle architecture in the amputated limb, which could not be predicted from short-term disuse studies.

ABSTRACT:

The purpose of this study was to determine: (1) whether individuals with unilateral transtibial amputations (ITTAs), who habitually disuse the quadriceps muscles of their amputated limb, provide an effective model for assessing the effects of long-term muscle disuse; and (2) the effects of such disuse on quadriceps muscle strength and neuromuscular function in this population. Nine ITTAs and nine controls performed isometric voluntary knee extensions in both limbs to assess maximal voluntary torque (MVT) and rate of torque development (RTD). The interpolated twitch technique and EMG normalised to maximal M-wave assessed neural activation, involuntary (twitch and octet) contractions assessed intrinsic contractile properties, and ultrasound images of the vastus lateralis assessed muscle architecture. Clinical gait analysis was used to measure knee kinetic data during walking at an habitual speed. ITTAs displayed 54-60% lower peak knee extensor moments during walking in the amputated than intact/control limbs, but the intact and control limbs were comparable for loading during walking and muscle strength variables, suggesting the intact limb provides a suitable internal control for comparison to the disused amputated limb. MVT and RTD were ∼60% and ∼75% lower, respectively, in the amputated than intact/control limbs. The differences in MVT appeared associated with ∼40% and ∼43% lower muscle thickness and neural activation, respectively, whilst the differences in RTD appeared associated with the decline in MVT coupled with slowing of the intrinsic contractile properties. These results indicate considerable changes in strength and neuromuscular function with long-term disuse, that could not be predicted from short-term disuse studies. This article is protected by copyright. All rights reserved.

KEYWORDS:

muscle atrophy; muscle strength; neural activation

PMID:
31773821
DOI:
10.1113/EP088087

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