Agreement between vertical ground reaction force and ground reaction force vector in five common clinical tests.

Mechanography is an innovative method to evaluate lower-limb dynamic muscle function. This technique is generally performed on force platforms that measure only the vertical component of ground reaction force (GRF). The underlying assumption is that medio-lateral and antero-posterior forces do not contribute significantly to the GRF in jumping and rising tests. The goal of this study was to establish the validity of this assumption. Fifteen healthy adults (mean age [SD]: 30 [11] years; mean height [SD]: 1.68 [0.12] m; mean body mass: 70 [18] kg) performed three repetitions of five different tests in the following order: multiple two-legged hopping, multiple one-legged hopping, single two-legged jump, heel-rise test and chair-rise test. An excellent agreement was found between peak GRF and peak vertical GRF. In each of the five tests, peak vertical GRF represented more than 99% of peak GRF. Moreover, the limits of agreement ranged between 0.05% (multiple two-legged hopping test) and 0.4% (heel-rise test) of the averaged peak force measurements. Therefore measuring only the vertical component of ground reaction force in healthy participants is appropriate for the five tests used in the present study.