Power of counter movement jumps with external load--coherence of three assessment methods

The purpose of this study was to evaluate the coherence between three different methods assessing the power driven from a counter movement jump (CMJ); the Powertimer 300-series contact mat (C-mat), the MuscleLab 4010 infrared mat (IR-mat) and the MuscleLab 4010 linear encoder (M-encoder), and to evaluate the test-retest reliability of the M-encoder.

Twenty-two males and 29 female, elite athletes performed two test sessions with three days in between. Each test session included counter movement jumps (CMJ) performed on a Smith-machine with external loads of 40 kg. Jump height and flight time were assessed with C-mat and IR-mat, and power was additionally assessed with C-mat. Variables analyzed from the M-encoder were average power (AP), average force (AV), average velocity (AV), and distance (D).

The results from the C-mat were systematically higher than the ones obtained from the M-encoder and IR-mat. The correlation between the C-mat, M-encoder and the IR-mat was strong (r(p)= 0.95-0.98). The results showed a high test-retest reliability for all indices assessed with the M-encoder, AP (r(p)= 0.97, p < 0.001; TE% = 3.9%), AF (r(p) = 0.99, p < 0.001; TE% = 1.4%). Furthermore, the AV had high values (r(p) = 0.94, p < 0.001; TE% = 2.9%) as well as D (r(p) = 0.87, p < 0.001; TE% = 5.4%).

It is important to use the same equipment in both pre- and post-testing, since all three methods were reliable, coherent but not interchangeable to each other.