Aim Vertical jump represents an important skill in many sports and its evaluation is proposed to assess lower limb strength. The Jump­and-Reach test is the most commonly used field­test. It measures, on a vertical surface, the difference between the heights reached by the fingers with the arm extended standing flatfooted and at the highest point of the flight phase. It is simple, no equipment is required, but unilateral swing of the arm, involvement of muscles beyond the lower limb and coordination are needed. The Squat Jump and the Countermovement Jump, with hands to the hips, are adopted to obtain a specific measure of lower limb strength. The Countermovement Jump with arm swing is proposed to assess a more natural jump performance. Unfortunately, it is impossible to measure the height of these jumps without devices, such as accelerometers, contact mats, force platforms and video-analysis. The Optojump (Microgate, Bolzano-Italy), an optical transmitting-receiving bars measurement system, is proposed to measure these jumps. The aim of this study is to assess the test­retest reliability of Squat Jump, Countermovement Jump and Countermovement Jump with arm swing measured by Optojump system. Moreover, the reliability of Jump­and­Reach test measured both by vertical surface and by Optojump and the agreement between these two methods are analysed.

Methods 31 healthy volunteers were recruited (16 F­15M). Inclusion criteria: age 20­29 years, absence of painful conditions in the last three months. Subjects with orthopaedic, vascular, rheumatological and/or neurological diseases affecting lower limb were excluded. Each subject performed squat jump, countermovement jump and countermovement jump with arm swing using Optojump. Furthermore, each participant performed jump­and­reach test and data were recorded by vertical surface (field­test) and by Optojump, simultaneously. Each jump was repeated three times during a single session (4 sessions in 2 days), with 20’’ rest between jumps and 5’ rest between different jumps’ test. The sequence of test was modified in each session. The interclass correlation coefficients and the standard error of measurement were calculated. The Bland-Altman method was used to assess the agreement between the two methods of measurement adopted for jump­and­reach.

Results Interclass correlation coefficients were Squat Jump = 0.969 (CI: 95% = 0.946–0.984, SEM = 1.91), Countermovement Jump = 0.969 (CI: 95% = 0.947–0.984, SEM = 1.7), Countermovement Jump with arm swing = 0.985 (CI: 95% = 0.973–0.992, SEM = 1.69), Jump­and­Reach (Optojump) = 0.989 (CI: 95% = 0.981–0.994,SEM = 1.56), Jump­and­Reach (vertical surface) = 0.982 (CI: 95% = 0.968–0.990, SEM = 2.91). Jump­and­Reach scores obtained by vertical surface were significantly higher than scores recorded by Optojump (p < 0.001). The correlation coefficient was very high (r = 0.92) but Bland­Altman analysis (Figure 1) showed a significant bias between two methods (mean = 12.36 cm, limits of agreement 2.63­22.09 cm +42,04%, limits of agreement 17.46%, 66.62%).

Conclusions The Optojump is a reliable device to measure Squat Jump, Countermovement Jump, Counter-movement Jump with arm swings and Jump­and­Reach. Also the Jump­and­Reach test measured by vertical surface showed a significant reliability but with scores higher than Optojump. A significative bias in the agreement between the two methods of Jump­and­Reach measurement was detected. This difference is probably due to some biomechanical aspects that require further investigations to better understand the impact of upper body structures on jump performance.

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Abstract O-32 Figure 1

Bland-Altman Analysis