Drop Jumps

Externally focused instructions specific to performance have shown to improve body mechanics (Gokeler et al., 2015; Welling, Benjaminse, Gokeler, & Otten, 2016). However, the effect of using an external focus instruction may have been more profound if the content of the instruction had been relevant to mechanics. Therefore, the present study examined the effects of externally fo-cused instructions specific to performance and externally focused instructions specific to body mechanics on mechanics and performance. Twenty-four adults (n = 12 males; n = 12 females) performed a series of drop jumps following external focus cues that were specific to performance and landing mechanics. Participants completed a drop jump followed by a maximal effort vertical jump. The initial contact, maximal angle, and range of motion at the knee in the sagittal and frontal plane motion were measured for mechanics and the height of the second vertical jump was measured for performance. The results suggest external focus instructions specific to performance are beneficial for performance, but not for improving landing mechanics. This suggests that external focus instructions must be specific to the contents of the instruction.

Objective: The purposes of this study were to investigate the comparison of some stretch-shortening cycle (SSC) parameters, and to correlate reactive strength index (RSI) scores from drop jumps (DJ) and sprint times (ST) among maturation groups according to peak height velocity (PHV). Methods: A total of 108 youth soccer players were included in this study (age: 13.0±1.5 years old; height: 162.7±12.1 cm; weight: 53.1±11.7 kg). Participants were divided into three groups (Pre-PHV, Mid-PHV and Post-PHV) according to calculation using the maturity offset equation. DJ tests from 20 and 40 cm drop heights (DH) and 30 m sprint tests were made by participants. RSI scores were taken during DJs. All tests were performed twice. One-way ANOVA and Welch ANOVA tests were performed to test differences between more than two independent groups for normally-distributed data. If a significant difference was found, Bonferroni and Games-Howell tests were performed for multiple comparisons, respectively. Pearson correlation coefficients were calculated for bivariate correlations between numeric variables, where appropriate. A value of p<0.05 was accepted as significant. Results: RSI scores of 20 cm DJ were significantly different among groups (p<0.001). RSI of 40 cm DJ of the Pre-PHV group was significantly different than the other groups (p<0.001). All maturation groups were significantly different in terms of sprint times (p<0.001). The RSI of 20 cm DH was correlated with 20 m ST in the Mid-PHV group. But RSI of 40 cm DH was correlated predominantly with 20 m ST in youth soccer (p<0.05). Conclusion: The main finding of this study was that 40 cm drop height and 20 m sprint distance are more optimal to be used to monitor SSC performances of youth soccer players during maturation.

Tsoukos, A, Veligekas, P, Brown, LE, Terzis, G, and Bogdanis, GC. Delayed effects of a low-volume, power-type resistance exercise session on explosive performance. J Strength Cond Res 32(3): 643-650, 2018-This study examined the delayed effects of a power-type training session on explosive performance. Seventeen well-trained male power and team sport athletes (age: 22.7 6 5.5 years, height: 181 6 8 cm, body mass: 80.7 6 8.6 kg, body fat: 9.2 6 1.7%, 1 repetition maximum (1RM) half-squat: 163 6 29 kg) performed 4 sessions (2 experimental and 2 control) 1 week apart in a randomized and counterbalanced order. Explosive performance was assessed before, 24 and 48 hours after a low-volume, power-type training session (5 3 4 jump squats at 40% 1RM with 3 minutes rest), as well as before and after 24 and 48 hours of rest (control). Dependent variables were as follows: countermove-ment jump (CMJ), reactive strength index (RSI) during a drop jump, leg press maximum isometric force, and rate of force development (RFD) at 3 time windows: 0-100, 0-200, and 0-300 milliseconds. Analysis of variance revealed no changes in the control conditions. In contrast after training, CMJ was improved by 5.1 6 1.0% and 3.0 6 1.0% at 24 and 48 hours, respectively, compared with baseline. The RSI improved by 10.7 6 2.1% only at 24 hours. The RFD increased at all time windows at 24 hours (range of improvement: 9.7 6 3.4% to 18.3 6 4.1%, p , 0.01). However, at 48 hours, improvement was only seen in RFD 0-100 (9.8 6 3.1%, p , 0.01). These findings suggest that a low-volume, power-type training session results in delayed enhancement of explosive muscle performance , which is greatest at 24 hours after the activity. Athletes are advised to perform power-type training 1 day before competition or a high-quality training session to improve their performances.

Backround. The present study assessed the relationship between various strength-power tests and maximal running velocity parameters.
Methods. Nine trained males were tested on four separate occasions. On the first occasion the maximum running velocity (MRV), stride rate (SR) and stride length (SL) were measured over 35 m. On the second occasion maximal vertical jumps [squat jump (SJ), standing broad jump (SJ), counter movement jump (CMJ) and drop jumps (DJ) from heights of 30, 50 and 80 cm] were performed on a force platform: On the third occasion the maximal bilateral isometric force (MBIF) of leg extensors and the force time characteristics (f-t 10-30%, f-t 10-60% and f-t 10-90%) were determined using a leg extension machine connected to a force plate. On the final fouth occasion peak anaerobic power was measured via repeated 6 s maximum cycle sprints. Pearson product-moment correlation coefficients were calculated for all the aformentioned parameters.
Results. The correlation coefficients showed that MRV correlated significantly with f-t 10-60%  and DJ30 (r = -0.73 and r =0.73, p<0.05 respectively).  In addition, SR and SL  showed significant, and critical for SR, relationship with f-t 10-60% (r = -0.82, p<0.01 and r = 0.75, p<0.05 respectively).
Conclusions. The present findings suggest that the ability to produce force quickly, as measured by the time to achieve 60% of maximum voluntary contraction is related to sprinting performance, with the coefficient of determination accounting for 53% of the variance in the data. These data also showed that sprinting ability is linked with drop jumping performance, especially the drop jump from a height of 30 cm. It is suggested that the above tests may prove useful in preparing and testing the sprinting ability and sprint specific strength levels.

Introduction. Drop jump is one of the most researched plyometric
exercises. Different drop heights were earlier investigated
for ground reaction forces, biomechanical analysis, and other
parameters. There has been no research into the influence
of drop height on maximum jump height during drop jump
among soccer players. Aim of Study. This study aimed to find
out the optimal drop height for maximum vertical jump height
in drop jumps. Material and Methods. The researchers selected
17 male soccer players (mean ± SD; age 21 ± 2 years, height
174 ± 8 cm, body mass 63 ± 5 kg, isometric leg strength 122 ±
± 18 kg) for the study. Drop jump from different heights (35 cm,
45 cm, 50 cm, 65 cm, and 72 cm) was investigated for jump height,
take-off force, take-off speed, impact force, maximum concentric
power, and peak speed. Results. Repeated measures ANOVA
revealed significant difference in jump height from different
drop height (F2.54,40.59 = 5.605, p = 0.004, partial η2 = 0.259). Posthoc
analyses through Bonferroni adjustment showed significant
differences between jump height from 35 cm box and 45 cm
box (t16 = 4.31, p = 0.001, d = 0.47) and 35 cm box to 72 cm box
(t16 = 3.52, p = 0.003, d = 0.60). However, no significant differences
could be observed in take-off force, impact force, maximum
concentric power, peak speed, and take-off speed from different
drop heights. Isometric leg strength were significantly correlated
with jump height from 35 cm (p = 0.014), 45 cm (p = 0.021) and
50 cm (p = 0.022) drop height. Conclusions. The study concludes
that to improve maximum jump ability of soccer players, box
height ranging around 65 cm to 72 cm may be selected for training
purposes and thus may help improve the body’s ability to convert
the momentum generated by a run to maximum vertical height.