Upper limb mechanical changes following short duration repetitive eccentric exertions.
BACKGROUND
Power hand tool use is considered a risk factor for upper extremity musculoskeletal disorders. It is unclear if submaximal eccentric activity inherent to power tool use adversely affects the mechanical properties of muscle.


METHODS
This study investigated in vivo changes in human upper limb dynamic mechanical properties following exposure to short-term repetitive submaximal eccentric exertions that are similar to operating an industrial power hand tool. Eighteen subjects (12 males and 6 females) were assigned to one of three exercise groups (isometric, eccentric or control) and exercised 10 min for 60 repetitions at 50% of isometric forearm supination maximum voluntary contraction. Supination strength and dynamic mechanical properties (stiffness, effective mass, and damping) of forearm rotation, modeled as a single-degree-of-freedom system during maximal exertion, were ascertained prior to exercise, immediately following exercise and 24 h later.


RESULTS
Strength decreased for the isometric (17%) (P < 0.05) and eccentric (34%) (P < 0.01) groups following exercise. Only the eccentric exercise group had a reduction in mechanical stiffness (53%) (P < 0.01) and effective mass (58%) (P < 0.05). The other groups had no changes in mechanical properties.


CONCLUSIONS
The change in mechanical properties following repetitive submaximal eccentric activity could negatively impact the ability of the arm to react to rapid forceful loading during repetitive industrial work activities and may indicate mechanical strain on the upper limb.
Department of Industrial Engineering, University of Wisconsin, Madison, WI 53706, USA.
Mary E
ME
Sesto
Robert G
RG
Radwin
Thomas M
TM
Best
Terry G
TG
Richard
D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004548:Elasticity; D015444:Exercise / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D009784:Occupational Diseases / Q000503:physiopathology / Q000517:prevention & control; D009929:Organ Size / Q000502:physiology; D010507:Periodicity; D005082:Physical Exertion / Q000502:physiology*; D013314:Stress, Mechanical; D034941:Upper Extremity / Q000502:physiology