Analyses of Countermovement Jump Performance in Time and Frequency Domains

Strength and dynamic balance performance in soccer players in the United States: age, sex, and bilateral differences

Quantification of asymmetries between the two limbs is informative in assessing the risk of injury and performance deficits, but there is a paucity of studies investigating the effects of age and sex on bilateral asymmetry in young soccer players. This cross-sectional study aimed to investigate the effects of age and sex on strength and dynamic balance in 7- to 24-year-old soccer players in the United States. A total of 174 young soccer players participated in the study (Age 7-9 years: 26 females and 16 males; Age 10-12 years: 32 females and 31 males; Age 13-17 years: 17 females and 25 males; Age >18 years: 13 females and 14 males). Jump displacement, peak force, and asymmetry during countermovement jump with arm swing and landing, peak force and asymmetry during push-up, and normalized reaching distances for upper and lower extremity reaching tests were quantified. Preferred legs and arms were defined as the preferred kicking leg or throwing arm. As age increased, both preferred and non-preferred sides demonstrated decreased landing forces, increased jump displacement, and increased normalized peak forces during push-ups in both males and females (p < 0.05). Males showed greater jump displacement, normalized landing forces, and normalized peak forces in push-ups compared to females in several age groups (p < 0.05). No significant differences were observed for asymmetry variables between ages or sexes, and on average, most bilateral asymmetry variables were less than 5%. Age was associated with strength but not dynamic balance performance in healthy soccer players in the United States. Male and female players demonstrated similar changes, and bilateral asymmetries were on average small. Soccer players may need more dynamic balance training over time as they progress to higher levels of competition. Landing technique training may be implemented for young soccer players to decrease the high impact landing forces and landing related injury risk. Asymmetries and their relationships with injury risk should be evaluated on an individual basis, as their relationships with age and sex were weak. Future longitudinal and cohort studies are warranted to further elucidate the relationship among strength, dynamic balance, and injury risk in soccer players.

Residual Effects of Same Day Lower Extremity Strength Training on Countermovement Jump Performance in Collegiate Women Athletes

Balancing of strength programming intensity with sport demands is necessary to avoid excessive workloads that could inhibit performance. To expand previous jump height focused literature, this study evaluated whether countermovement jump (CMJ) movement strategies, including eccentric characteristics, might reveal CMJ execution strategy shifts to achieve similar afternoon CMJ height following a morning resistance training session (RTS). Fifteen collegiate women's soccer and volleyball athletes (18-24 years, 73.6 ± 8.4 kg, 1.74 ± 0.19 m) participating in an offseason RTS completed five CMJs during two afternoon sessions (48 h apart), one 4-6 h post morning RTS, and one on a rest day. The RTS consisted of 2 sets of 10 repetitions at 70-80% 1RM for the back squat, the front squat, and the forward lunge. Vertical ground reaction forces were recorded from which 13 outcome measures describing elements of the eccentric and concentric CMJ phases were computed. No significant differences in jump height (p = 0.427, d = 0.17) or outcome measures (p = 0.091-0.777, d = -0.07-0.21) between sessions with exception of a significant concentric phase time decrease (p = 0.026, d = 0.23) following the RTS were identified. Given the magnitude of the mean concentric phase time change (0.01 s), the result likely has limited practical meaning. As these results confirm previous CMJ height literature, practitioners have further evidence that a morning RTS does not interfere or enhance afternoon CMJ performance in athletic women.

Effects of a Strength and Conditioning Offseason Program on Countermovement Jump Ground Reaction Forces in Division I American Football Players

ABSTRACT

Gillen, ZM, Burch, RF, Saucier, DN, Strawderman, L, Luczak, T, Piroli, A, Petway, AJ, and Rath, T. Effects of a strength and conditioning offseason program on countermovement jump ground reaction forces in Division I American football players. J Strength Cond Res 38(3): e86-e95, 2024-The purpose of this study was to examine the effects of a 10-week strength and conditioning offseason program on the ground reaction forces (GRFs) of American football players during single-leg and double-leg countermovement jumps (SLJ and CMJ, respectively). Each subject visited the laboratory twice, once for preoffseason and once for postoffseason testing. During each visit, subjects performed CMJs and SLJs for each leg. Ground reaction forces were collected by force plates to quantify unweighting, braking, propulsive, and performance metrics for each jump. In addition, an efficiency index was calculated for each jump to examine changes in vertical jump efficiency. Dependent samples t tests compared all CMJ metrics. Two-way repeated measures analyses of variance (leg × time) compared all SLJ metrics. An alpha level of p ≤ 0.05 was considered statistically significant. For the CMJ, propulsive phase duration decreased due to the program ( p = 0.007), whereas peak braking power, peak propulsive power, mean propulsive force, and jump height increased ( p ≤ 0.012). For the SLJ, peak braking power, force at the low position, braking rate of force development, eccentric force, peak propulsive power, mean propulsive force, and jump height increased in both legs ( p ≤ 0.044). The efficiency index increased for the CMJ and the SLJ for both legs ( p ≤ 0.016). This study demonstrated that SLJ and CMJ vertical jump performance significantly increases in as few as 10 weeks of offseason strength and conditioning. Strength and conditioning programming may effectively increase vertical jump performance, as assessed by GRFs, which can be used as a simple indicator regarding changes in athletic performance.

Reliability and Validity of the Portable KForce Plates for Measuring Countermovement Jump (CMJ)

Physical fitness is of great significance to athletes in both single-player and team sports. The countermovement jump (CMJ) is one of the most commonly applied jump tests for assessing the mechanical capacities of the lower extremities. The KForce Plates system is a portable force platform that sends action-time audio and visual biofeedback to a smartphone or tablet through the KForce application, making it a suitable instrument for assessing the CMJ. The aim of the present study was to evaluate the test–retest reliability and validity of the portable force platform (KForce Plates) in the evaluation of the CMJ in collegiate athletes compared to a validated application, My Jump 2. Thirty-four collegiate professional athletes, deriving from various sports backgrounds, participated in the present study. The CMJs were reported with the portable KForce Plates and the simultaneous use of the ‘My Jump 2’ application using an iPhone 13 between days 1 and 7. Our findings revealed high test–retest reliability (ICC = 1.00 and ICC = 0.99) in-between measurements. High correlations were monitored amongst the portable KForce plates and the My Jump 2 application for measuring the CMJ (r = 0.999, p = 0.001). The Bland–Altman plot exhibits the limits of agreement amongst the portable KForce plates and the My Jump 2 application, where the bulk of the data are within the 95% CIs with an agreement of ≈1 cm. Our findings suggest that the portable KForce Plates system is a reliable and valid instrument and, therefore, can be used by experts in the sports field.

The validity of using one force platform to quantify whole-body forces, velocities, and power during a plyometric push-up

Background

Previous studies have typically measured velocity and power parameters during the push-up, either using one or two force platforms. The purpose of the study was to compare the force, velocity, and power parameters between the one-force-platform method and the two-force-platform method during plyometric push-ups.

Methods

Thirty-four physically active young adults participated in the study to perform the plyometric push-up. For the two-force-platform calculation method, the forces applied to the feet and hands were both measured. For the one-force-platform calculation method, the forces applied to the feet were assumed to be constant, while the forces applied to hands were measured by one force platform. Whole-body linear velocities were calculated based on the impulse and momentum theorem. Whole-body power was calculated as the product of the whole-body forces and velocities.

Results

The one-force-platform method overestimated the whole-body velocities and power compared with the two-force-platform method (1.39 ± 0.37 m/s vs. 0.90 ± 0.23 m/s, Cohen’s d = 1.59, p < 0.05; 1.63 ± 0.47 W/body weight vs. 1.03 ± 0.29 W/body weight, Cohen’s d = 1.49, p < 0.05). These differences were caused by the decreased forces applied to the feet compared to the initial value throughout most of the push-up phase. Large to perfect correlations (r = 0.55 – 0.99) were found for most variables between the two-force-platform and one-force-platform methods. Previous findings of push-up velocities and power using the two-force-platform and one-force-platform methods should be compared with caution. While the two-force-platform method is recommended, linear regression equations may be used to predict velocities and power parameters obtained from one force platform.

Conclusions

For those professionals who need to accurately quantify kinetic variables during the plyometric push-up, the two-force-platform method should be considered.

Optimizing the Explosive Force of the Elite Level Football-Tennis Players through Plyometric and Specific Exercises

The aim of the research was to implement an athletic program to improve the explosive force in order to optimize physical fitness at the level of elite football-tennis players and evaluate the progress made through specific tests using the Opto Jump. The research included 10 elite European and world-class players, on whom an experimental program was applied in order to improve the explosive force of the limbs in conditions of speed, endurance, and dynamic balance. Study tests: five vertical jumps on the spot, on the left/right leg; five back and forth jumps on the left/right leg; five left/right side jumps on the left/right leg; vertical jumps on both legs 60 s; BFS vertical jumps. For each test, the following parameters specific to the explosive force were statistically analyzed: contact time (s); flight time (s); jump height (cm), jump power (w/kg); RSI—Reactive Strength Index, defined as Height (m/s). In the study, the average value of the parameters specific to the jumps performed in each test was taken into account. During the study, the tests were performed and processed on the Opto Jump device and software. In all tests of the experiment monitored through Opto Jump, significant progress was made in the final test compared to the initial one, which demonstrates the efficiency of the physical training program implemented for the development of explosive force, with an impact on the sports performance of elite players. The most relevant results obtained for the left leg regarding the improvement of the explosive force of the lower limbs materialized in the jump height parameter was in the test of five vertical jumps on one leg on the spot, and for the right leg in the tests of: five back and forth jumps and five left/right side jumps. The most significant advances in the study were in the tests, in descending order of their weight: 60 s vertical jumps on both legs; five back-and-forth jumps and five left/right side jumps, five vertical jumps on one leg standing, and BFS vertical jumps.