Table 1: Examples of Intrinsic and Extrinsic Factors

INTRINSIC FACTORS

EXTRINSIC FACTORS

Age

Magnitude, direction, duration, rate, and lack of variability of work-related external forces affecting tissue stress/strain history

Gender

Number, frequency and duty cycle of work-related loading cycles affecting tissue stress/strain history

Tissue anatomy - heritable factors, changes due to tissue injuries during childhood/adolescence

Work-related postural requirements affecting tissue stresses/strain history

Tissue physiology-healing/remodeling potential; response to chronic loading

Availability of rest days

Tissue state-state of hypertrophy/atrophy/remodeling as it affects relevant tissue physical capacities

Leisure/commuting activities engendering tissue stress/strain history

Muscle recruitment strategies, related functional biomechanics

 

Response to psychological stress

 

Response to pain state

 

Soft tissue injury triggers a complex cascade of events involving an inflammatory response, which marks the first phase of the healing response, a proliferative stage, followed by a remodeling phase (Gelberman, Goldberg, An, & Banes, 1988). Uneventful transitioning through these phases usually requires a temporary reduction in physical loading because of pain or discomfort, followed by a gradual increase in physical loading to stimulate healing and subsequent tissue remodeling processes. The problem is not so much increasing physical loading again, but increasing it at a rate that does not exacerbate symptoms or, worse, cause re-injury. In some jobs workers may have considerable discretion over how and when they choose to increase the magnitude and duration of loading after injury or overuse syndromes appear so as not to aggravate symptoms. But in other jobs they may have little control over such matters, thereby increasing the risk of developing more chronic syndromes. 'Work-hardening' programs are specifically designed to minimize this risk by prescribing graduated physical training regimens to better prepare tissues for the type of work to be done.

It should not be surprising that sudden increases in activity associated with switching to a new and more physically demanding work can trigger overuse syndromes. It is always possible for an individual to increase physical loading too rapidly for tissue repair and adaptation mechanisms to be able cope with the new demands. Classic examples of this are the millions of unnecessary sports-related injuries that occur every year at all ages due to training errors. These errors are simply caused by an athlete increasing the intensity or duration of their training too rapidly for the tissue to adapt to the new regimen. Such injuries and conditions are preventable by better athlete and



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