Optojump next

Jump height was calculated at the nearest 0.1 cm from flight time measured with an infrared timing system (OptojumpNext, Microgate, Bolzano, Italy). Because the take-off and landing positions can affect the jump flight, strict instructions were addressed to all participants to keep their legs straight during the flight time of the jump. The subjects started from an upright standing position, made a downward movement until approximating a knee angle of 90°, and subsequently began to push off at maximal velocity. All participants completed 5 maximal CMJs, with their hands on their hips, separated by 1 min rest. The highest and the lowest values were discarded, and the resulting average value was kept for analysis. The specific warm-up consisted of two sets of 10 squats without external load, 5 submaximal CMJs, and 3 maximal CMJs. The test–retest reliability was as follows: intraclass correlation coefficient (ICC) was 0.93 (95% confidence interval (CI): 0.86; 0.97), and the coefficient of variation (CV) was 1.7%.

Muscle functional capabilities of the lower limbs were assessed during a bout of 20 s of maximal hopping (repeated jumps) before (rested state, PRE) and after (fatigued state, POST) the running exercise (Joseph et al., 2013 (link)). Participants were asked to jump as high and as often as possible over the whole 20 s bout. Contact time (t_c), aerial time (t_a) and jump frequency (f = 1/[t_a + t_c]) were measured using optoelectric cells (OptoJumpNext, Microgate, Bolzano, Italy) positioned ~1-m apart on level ground, with a time resolution of 1 ms. In order to maximize the contribution of plantar flexor muscles and minimize the contribution of knee extensor muscles, the jumps were performed without bending the knees using verbal instructions and a knee brace locked in a fully extended position (GenuControl, Thuasne Sport). Average and maximum power (in W·kg⁻¹) and limb stiffness (kl_eg, in N·m⁻¹) were calculated based on previous validated computations using t_c and t_a (Bosco et al., 1983 (link); Dalleau et al., 2004 (link)), following equations 4, 5, and 6:
$\text{h}=\raisebox{1ex}{$\text{g}\times {t_a}^2$}\!\left/ \!\raisebox{-1ex}{$8$}\right.$
$\text{P}=\raisebox{1ex}{$({\text{g}}^2\times t_a\times [t_a+t_c])$}\!\left/ \!\raisebox{-1ex}{$4\times t_c$}\right.$
$k_{leg}=\raisebox{1ex}{$(\text{m}\times \Pi \times [t_a+t_c])$}\!\left/ \!\raisebox{-1ex}{${t_c}^2\times (\raisebox{1ex}{$t_a+t_c$}\!\left/ \!\raisebox{-1ex}{$\Pi $}\right.\raisebox{1ex}{${-}^{t_c}$}\!\left/ \!\raisebox{-1ex}{$4$}\right.)$}\right.$
where g is the gravitational attraction (g = 9.81 m·s⁻¹), m is the mass of the participant (in kg).

Countermovement jumps (CMJ) and squat jumps (SJ) were done before and after the RSA test, using an infrared system (Optojump Next, Microgate, Bolzano, Italy). Participants had to keep their hands on their hips to eliminate the influence of arm movement on jump performance. Every player did two jumps in each modality before (with 2 min of recovery between jumps) and after the RSA test. The best of them was selected for the statistical analysis.
In the same way, players carried out the fifteen seconds maximal jump test to assess the performance deterioration in their jumping action. For this test, participants had to stand upright with feet apart at shoulder width and with their hands on their hips in the same way as in the CMJ. At the start signal, subjects flexed their knees and carried out a maximum performance of jumps for 15 s, landing with both feet at the same time. The maximum height in cm, % Dec (100–(mean jump/best jump×100)) [12] (link) and the output power [(62.5×50.3×jump height+body mass)–2184.7]×number of jumps] [50] (link) were calculated for this test.

After the standardized warm-up, the players performed three bilateral CMJ and three unilateral Abalakov jumps (ABK) with each limb, separated by 45 s of passive recovery (Núñez et al., 2018 (link)). During the CMJ, all participants were instructed to place their hands on their hips, which was followed by a vertical jump at maximal effort and landing in a vertical position, with their knees being flexed after landing (Sáez de Villarreal et al., 2015 (link)). However, during ABK, the swinging of the arms was allowed. All the jumps were performed on a platform with infrared rays (Optojump Next; Microgate^®, Bolzano, Italy), and the jump height (cm) was recorded. The best of the performances of each test was selected for the subsequent statistical analysis.

CMJ was calculated from flight time, measured by an optical system (Optojump next, Microgate, Bolzano, Italy). The students were asked to jump as high as possible with their arms on their hips (akimbo) maintaining the same body position during take-off and landing [42 (link)]. Three jumps were performed interspersed with 30 s of rest, and the best performance was used as a baseline value. CMJ was measured again one minute after the end of the repeated shuttle-sprint running test.

The first performance test following the re-warm-up interventions was the CMJ (OptoJump Next, Microgate, Bolzano, Italy). Players performed 3 maximum CMJs with arms akimbo while 45 s rest was given between attempts. During CMJs, players had the instruction to jump as high as possible. Following each jumping attempt, researchers informed players about the jump height (cm) in order to motivate them for a greater effort. The mean CMJ height from all 3 attempts was used for the statistical analysis [22 (link)]. Power and power relative to body mass were also calculated [23 (link)]. The intra class correlation coefficient (ICC) for CMJ height, power, and power relative to body mass were 0.989 (95% confident intervals (CI): Lower = 0.957, Upper = 0.997), 0.980 (95% CI: Lower = 0.985, Upper = 0.990), and 0.981 (95% CI: Lower = 0.978, Upper = 0.991), respectively.

For SJs performed during RSJ tests and F-v and P-v relationships assessment, force, velocity, and power developed during the push-off phase were computed using Eqs 1–3. The jump height was determined from fundamental laws of dynamics and aerial time (Asmussen and Bonde-Petersen, 1974 (link)), the latter being obtained using an infrared timing system (OptoJumpNext, Microgate, Bolzano, Italy). For each participant, the F-v and P-v relationships were determined from F, v, and P values obtained from the 5 loading SJ conditions and were used to extrapolate F₀ and v₀, the y and × intercept of the F-v relationship, respectively. Then, P_max was computed as (Samozino et al., 2012 (link)):
For each of the 10 RSJ conditions, R_Fv was computed as the ratio between the force developed (expressed relative to F₀) and the velocity (expressed relative to v₀). Exhaustion was defined as the inability to perform three consecutive jumps above 95% of the targeted jump height. Strength-endurance was quantified by (i) the maximum repetitions (SJ_Rep) and (ii) the cumulated mechanical work output (W_tot) associated to SJ_Rep. SJ_Rep corresponded to all repetitions preceding exhaustion, excluding the three jumps below the limit of 95% of the targeted performance and W_tot was computed as the sum of the mechanical work of all repetitions of SJ_Rep.