Effects of age and sex on shoulder biomechanics and relative effort during functional tasks
Introduction
Maximal voluntary torque and power of ankle, knee, and hip extensor muscles decrease with increasing age by up to 16% per decade starting at age 30 (Danneskiold-Samsøe et al., 2009, Harbo et al., 2012, Hortobágyi et al., 1995, Pearson et al., 2002, Reid and Fielding, 2012, Vandervoort, 1992). Although less extensively documented, age also affects the shoulder complex. Maximal voluntary isometric, eccentric and concentric shoulder abduction, flexion and internal/external rotation torques decline up to 25% in old compared to young adults (Danneskiold-Samsøe et al., 2009, Gallagher et al., 1996, Lindle et al., 1997, Murray et al., 1985). The age-related decline in maximal upper extremity torque is greater at the shoulder, followed by reductions at the elbow and wrist joint (Harbo et al., 2012). Age-related losses in concentric and eccentric peak torque occur in both sexes although reductions tend to be greater in older males than females (Danneskiold-Samsøe et al., 2009).
The age-related reductions in maximal voluntary shoulder torques and powers could increase the effort needed to perform activities of daily living (ADLs). Relative effort is the magnitude of torque used in an ADL task as percentage of the available maximal isokinetic torque. According to this concept, sarcopenic and weakened muscles work at a high relative effort, as such muscles operate near maxima of force and velocity, with speed of contraction also affected by age (Reid and Fielding, 2012). In tasks involving the lower extremities, healthy old adults perform several ADLs such as stair ascent and descent, and chair rising at a relative effort around 80% (Hortobágyi et al., 2003). Considering the large reductions in maximal shoulder torques and the increasing prevalence of shoulder pain over age 50 (McBeth and Jones, 2007, Picavet and Schouten, 2003, Vidt et al., 2016), it is conceivable that healthy old adults would lift and place objects, reach with and without a load, and perform precision tasks with the shoulder abducted, i.e., hair combing, at a high relative effort. The sex-related difference in torque reduction could result in women performing at lower relative effort than men due to a better preservation of maximal voluntary torque. Despite the relevance of relative effort for prevention or reduction of dysfunction and pain, to the best of our knowledge the magnitude of relative effort has not yet been determined in the shoulder during ADLs.
The purpose of the present study was to determine for the first time the relative effort in ADLs involving the shoulder joint in healthy young and older adults. The secondary aim was to determine the effects of sex and movement velocity on relative effort. We quantified the torques during ADLs by inverse dynamics and expressed these efforts relative to the appropriate maximal voluntary isokinetic torque. We hypothesized that relative effort would increase with age and that a greater effort would be present in tasks executed at a high movement velocity. Finally we expected a greater relative effort in men than in women.
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Participants
Healthy young (n = 10) and older adults (n = 10) participated in the study (Table 1). Inclusion criteria were: age 20–30 or over 55 years and the ability to read and understand Dutch and give an informed consent. Exclusion criteria were: diagnosed upper extremity pathologies that could interfere with the measurement, shoulder pain, diagnosed rheumatic diseases, a history of severe shoulder trauma within the previous two years (e.g. fracture, luxation), dementia or other psychiatric disorders.
Anthropometric measurements
Older compared with young participants were shorter (p = 0.020), had higher body mass index (p = 0.010) but were not different in body mass (p = 0.250).
Isokinetic measurements
Table 2 shows the maximal isokinetic shoulder torques. One person of the older group could not perform during isokinetic flexion at 90°/s.
The peak torques at 60 and 90°/s velocity were not statistically different within groups (all p ≥ 0.09). Results are thus presented for the 90°/s condition only. Shoulder abduction and flexion isokinetic
Discussion
The aim of this study was to determine the magnitude of the relative effort in the shoulder joint during ADL tasks in healthy young and older adults. As hypothesized relative effort increased with age, and with movement velocity but only during internal/external rotation and hair-middle tasks. A trend towards a greater relative effort was observed in abduction and reaching tasks. Sex did not affect relative effort in either age group.
The ∼52% age-related decrease in maximal voluntary isokinetic
Conclusions
In conclusion, healthy old adults perform most ADL tasks involving the shoulder joint with an effort of 52% of the maximal available ability, nearly twice the level in young adults, reaching values over 40% in activities performed overhead and over 60% in abduction and reaching tasks. The large reductions in maximal shoulder torque and the concomitant increase in relative effort during many ADLs could contribute to the high prevalence of musculoskeletal pain and shoulder dysfunction in old age.
Conflicts of interest
None.
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