menu ☰
menu ˟

Dynamic activity of the upper limb: effects on shoulder fatigue and discomfort


Browne, Aleksandra;

Institution: University of Limerick
Subject Keywords: musculo-skeletal disorders; MSDs; Ireland;
Topic: Chronic Conditions
Back pain
Catalogue: Research and Evaluation
Type: Article
Region: Republic of Ireland

Musculo-Skeletal Disorders (MSDs) of back pain and upper limbs are the
most common occupational injury group in Ireland (HSA, 2007). Across
Europe upper limb related MSDs account for over 45% of the total number of
reported cases of occupational ill health and injuries (EUROSTAT, 2004).
MSD risk factors include poor posture, repetitive or forceful movements, fast
paced work, vibration and poor ergonomic conditions, and affect muscles,
tendons, ligaments and blood circulation. High task repetition can lead to
residual fatigue, which over time can result in damage to tissues. But the role
of repetition can often be overly simplified in job evaluation and in the study
of its relationship with occupational MSDs. This thesis focuses on the role of
dynamic loading of the upper limb (with emphasis on the shoulder) as part
of a broader interpretation of repetition as a risk factor for upper limb MSDs.
Two case studies and five laboratory experiments were conducted. The case
studies demonstrated high levels of muscle activity and movement
variability. This thesis proposes that dynamic loading of the upper limb is
multifactorial comprising cycle time, movement frequency, muscle activity
variability, work/rest regime and posture variability. Quantitative testing
(using electromyography and electrogoniometers) as well as qualitative
testing (discomfort) methods was used to study musculoskeletal strain. The
laboratory experiments tested combinations of these factors at various levels
to test for main effects. Taguchi methods were used to model the effects of
physical factors on the perception of discomfort in the shoulder region.
The studies for the distal part of the upper limb revealed that high
movement frequency within the shoulder’s safe range of motion (0-40°
flexion, 0-30°) abduction did not increase the average electrical activity of the
forearm muscles above the level of 50%MVE, even for the heaviest tasks of
load lifting. This suggests that the shoulder muscles may not be affected by
heavy loading in the hands as anticipated.
Results from collective study of shoulder movement frequencies, work/rest
regimes, postures and loads using a Taguchi experiment design and
regression analyses were used to test and model shoulder discomfort effects.
The findings of low levels of EMG fatigue recorded across many of the
experimental conditions indicate that for the Upper Trapezius high
movement frequency dynamic contractions may affect the rate of the Motor
Unit (MU) recruitment in order to protect the muscle from overloading, at
least in short duration treatments. There is a need to further investigate the
effects of interactions of repetition with other factors on MU recruitment
patterns in the muscles of the upper limb.

Suggested citation:

Browne, Aleksandra; . () Dynamic activity of the upper limb: effects on shoulder fatigue and discomfort [Online]. Available from: [Accessed: 19th November 2019].


View your saved citations and reading lists


Click here to view all the resources gathered from this organisation's website.