Document Type

Article

Language

eng

Publication Date

8-2015

Publisher

Springer

Source Publication

Clinical Orthopaedics and Related Research

Source ISSN

0009-921X

Abstract

Background

Muscle fatigability can increase when a stressful, cognitively demanding task is imposed during a low-force fatiguing contraction with the arm muscles, especially in women. Whether this occurs among older adults (> 60 years) is currently unknown.

Questions/purposes

We aimed to determine if higher cognitive demands, stratified by sex, increased fatigability in older adults (> 60 years). Secondarily, we assessed if varying cognitive demand resulted in decreased steadiness and was explained by anxiety or cortisol levels.

Methods

Seventeen older women (70 ± 6 years) and 13 older men (71 ± 5 years) performed a sustained, isometric, fatiguing contraction at 20% of maximal voluntary contraction until task failure during three sessions: high cognitive demand (high CD = mental subtraction by 13); low cognitive demand (low CD = mental subtraction by 1); and control (no subtraction).

Results

Fatigability was greater when high and low CD were performed during the fatiguing contraction for the women but not for the men. In women, time to failure with high CD was 16 ± 8 minutes and with low CD was 17 ± 4 minutes, both of which were shorter than time to failure in control contractions (21 ± 7 minutes; high CD mean difference: 5 minutes [95% confidence interval {CI}, 0.78–9.89], p = 0.02; low CD mean difference: 4 minutes [95% CI, 0.57–7.31], p = 0.03). However, in men, no differences were detected in time to failure with cognitive demand (control: 13 ± 5 minutes; high CD mean difference: −0.09 minutes [95% CI, −2.8 to 2.7], p = 1.00; low CD mean difference: 0.75 minutes [95% CI, −1.1 to 2.6], p = 0.85). Steadiness decreased (force fluctuations increased) more during high CD than control. Elevated anxiety, mean arterial pressure, and salivary cortisol levels in both men and women did not explain the greater fatigability during high CD.

Conclusions

Older women but not men showed marked increases in fatigability when low or high CD was imposed during sustained static contractions with the elbow flexor muscles and contrasts with previous findings for the lower limb. Steadiness decreased in both sexes when high CD was imposed.

Clinical Relevance

Older women are susceptible to greater fatigability of the upper limb with heightened mental activity during sustained postural contractions, which are the foundation of many work-related tasks.

Comments

Accepted version. Clinical Orthopaedics and Related Research, Vol. 473, No. 8 (August 2015): 2568-2577. The final publication is available at Springer: DOI. © 2015 The Association of Bone and Joint Surgeons. Used with permission.

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