Kristian Thorborg's Phd Thesis

Strength data obtained by HHD can be used clinically in different ways. One possibility is to use
normative values. However, normative values do often not exist for different age groups and
levels of physical activity, and is therefore typically not an option. Another possibility is to use the
unaffected limb as a control. A lower limb symmetry index (LSI) can then be calculated by dividing
the strength of the affected limb by the unaffected limb.[76] Generally, it has been suggested that
lower-extremity strength deficits of less than 10% on the injured side compared to the uninjured
side should be considered the clinical milestone before returning an athlete to sport following an
injury.[76,77] More specifically, the achievement of a hip ADD/ABD ratio of more than 90% and an
hip ADD strength equal to that of the contralateral side has been recommended before returning
to sport after an adductor strain.[78] However, Thorborg et al.[70] showed, that eccentric hip ADD
symmetry cannot be assumed in injury-free soccer players. In fact, the dominant side was 14%
stronger than the non-dominant side with regards to eccentric hip ADD strength, although hip ABD
strength was similar. This finding of asymmetric eccentric hip ADD strength in injury-free soccer
players, between the dominant and non-dominant leg,[70] indicates that using contralateral
eccentric hip ADD strength as a reference-point for muscle recovery may be questionable.
Strength ratios, such as the hip ADD/ABD strength ratio, have previously been used for research
purposes, and seem to be a relevant measure of hip strength,[48] especially in athletes with
bilateral groin symptoms, where the contralateral limb cannot be used as a reference point. For
clinical evaluation of the individual athlete, the obvious advantage is that this testing method does
not require any age, limb-length or weight adjustment, since the player can act as his own control.
This makes the testing method ideal for quick assessments in the busy clinical situation. However,
the reliability of such ratio’s are often not reported. Just as with the LSI, a ratio is the result of two
tests, including the individual measurement variation of each test. These measures are therefore
often less reliable, compared to one test or movement direction, and measurement variation is
increased.
Patient-reported outcome questionnaires
There is a general consensus that Patient-Reported Outcomes (PROs) should serve as the gold
standard in the assessment of musculoskeletal conditions, where the patient’s perspective and
health-related quality of life are of primary interest.[4,79-81] A PRO is any report coming directly
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