Establishing Phase Definitions for Jump and Drop Landings and an Exploratory Assessment of Performance-Related Metrics to Monitor During Testing

ABSTRACT

Harry, JR, Simms, A, and Hite, M. Establishing phase definitions for jump and drop landings and an exploratory assessment of performance-related metrics to monitor during testing. J Strength Cond Res 38(2): e62-e71, 2024-Landing is a common task performed in research, physical training, and competitive sporting scenarios. However, few have attempted to explore landing mechanics beyond its hypothesized link to injury potential, which ignores the key performance qualities that contribute to performance, or how quickly a landing can be completed. This is because a lack of (a) established landing phases from which important performance and injury risk metrics can be extracted and (b) metrics known to have a correlation with performance. As such, this article had 2 purposes. The first purpose was to use force platform data to identify easily extractable and understandable landing phases that contain metrics linked to both task performance and overuse injury potential. The second purpose was to explore performance-related metrics to monitor during testing. Both purposes were pursued using force platform data for the landing portion of 270 jump-landing trials performed by a sample of 14 NCAA Division 1 men's basketball players (1.98 ± 0.07 m; 94.73 ± 8.01 kg). The proposed phases can separate both jump-landing and drop-landing tasks into loading, attenuation, and control phases that consider the way vertical ground reaction force (GRF) is purposefully manipulated by the athlete, which current phase definitions fail to consider. For the second purpose, Pearson's correlation coefficients, the corresponding statistical probabilities ( α = 0.05), and a standardized strength interpretation scale for correlation coefficients (0 < trivial ≤ 0.1 < small ≤ 0.3 < moderate ≤ 0.5 < large ≤ 0.7 < very large) were used for both the group average (i.e., all individual averages pooled together) and individual data (i.e., each individual's trials pooled together). Results revealed that landing time, attenuation phase time, average vertical GRF during landing, average vertical GRF during the attenuation phase, average vertical GRF during the control phase, vertical GRF attenuation rate, and the amortization GRF (i.e., GRF at zero velocity) significantly correlated with landing performance, defined as the ratio of landing height and landing time ( R ≥ ± 0.58; p < 0.05), such that favorable changes in those metrics were associated with better performance. This work provides practitioners with 2 abilities. First, practitioners currently assess jump capacity using jump-landing tests (e.g., countermovement jump) with an analysis strategy that makes use of landing data. Second, this work provides preliminary data to guide others when initially exploring landing test results before identifying metrics chosen for their own analysis.

FIFA 11+ Kids program effects on jump kinetics in soccer players - A randomized controlled clinical trial

This study aimed to analyse the effects of the FIFA 11+ Kids programme on jump kinetics in soccer players. Twenty-four athletes (aged 9-11 years) were randomly allocated to the following groups: 1) the FIFA 11+ Kids programme (FT, n = 12), and 2) control training (CT, n = 12). Kinetic assessments of vertical jump (VJ), drop landing (DL), and anterior jump + maximum vertical jump (AJ) were performed on a force platform before and after eight weeks of training. Post-intervention impulse peak force and maximum impulse force (VJ) were significantly greater than the baseline values in the FT group (P < 0.001). Post-intervention landing peak force values for the first and second landings (DL) were significantly greater than the baseline values in the FT group (P = 0.01 and P = 0.05, respectively). Post-intervention landing peak force in the first landing (AJ) was significantly greater than the baseline values in the FT group (P = 0.005). The FT was effective in improving the impulsion performance during VJ. However, it increased the landing forces during DL and VJ.

Relationship between Football-Specific Training Characteristics and Tibial Bone Adaptation in Male Academy Football Players

We examined the relationship between football-specific training and changes in bone structural properties across a 12-week period in 15 male football players aged 16 years (Mean ± 1 SD = 16.6 ± 0.3 years) that belonged to a professional football academy. Tibial scans were performed at 4%, 14% and 38% sites using peripheral quantitative computed tomography immediately before and 12 weeks after increased football-specific training. Training was analysed using GPS to quantify peak speed, average speed, total distance and high-speed distance. Analyses were conducted with bias-corrected and accelerated bootstrapped 95% confidence intervals (BCa 95% CI). There were increases in bone mass at the 4% (mean ∆ = 0.15 g, BCa 95% CI = 0.07, 0.26 g, g = 0.72), 14% (mean ∆ = 0.04 g, BCa 95% CI = 0.02, 0.06 g, g = 1.20), and 38% sites (mean ∆ = 0.03 g, BCa 95% CI = 0.01, 0.05 g, g = 0.61). There were increases in trabecular density (4%), (mean ∆ = 3.57 mg·cm^-3, BCa 95% CI = 0.38, 7.05 mg·cm^-3, g = 0.53), cortical dentsity (14%) (mean ∆ = 5.08 mg·cm^-3, BCa 95% CI = 0.19, 9.92 mg·cm^-3, g = 0.49), and cortical density (38%) (mean ∆ = 6.32 mg·cm^-3, BCa 95% CI = 4.31, 8.90 mg·cm^-3, g = 1.22). Polar stress strain index (mean ∆ = 50.56 mm³, BCa 95% CI = 10.52, 109.95 mm³, g = 0.41), cortical area (mean ∆ = 2.12 mm², BCa 95% CI = 0.09, 4.37 mm², g = 0.48) and thickness (mean ∆ = 0.06 mm, BCa 95% CI = 0.01, 0.13 mm, g = 0.45) increased at the 38% site. Correlations revealed positive relationships between total distance and increased cortical density (38%) (r = 0.39, BCa 95% CI = 0.02, 0.66), and between peak speed and increased trabecular density (4%) (r = 0.43, BCa 95% CI = 0.03, 0.73). There were negative correlations between total (r = -0.21, BCa 95% CI = -0.65, -0.12) and high-speed distance (r = -0.29, BCa 95% CI = -0.57, -0.24) with increased polar stress strain index (38%). Results suggest that despite football training relating to increases in bone characteristics in male academy footballers, the specific training variables promoting adaptation over a 12-week period may vary. Further studies conducted over a longer period are required to fully elucidate the time-course of how certain football-specific training characteristics influence bone structural properties.

Validation of Instrumented Football Shoes to Measure On-Field Ground Reaction Forces

Ground reaction forces (GRF) have been widely studied in football to prevent injury. However, ambulatory tools are missing, posing methodological limitations. The purpose of this study was to assess the validity of an innovative football shoe measuring normal GRF (nGRF) directly on the field through instrumented studs. A laboratory-based experiment was first conducted to compare nGRF obtained with the instrumented shoe (IS) to vertical GRF (vGRF) obtained with force platform (FP) data, the gold standard to measure vGRF. To this aim, three subjects performed 50 steps and 18 counter-movement jumps (CMJs). Secondly, eleven subjects completed running sprints at different velocities on a football field, as well as CMJs, while wearing the IS. Good to excellent agreement was found between the vGRF parameters measured with the FP and the nGRF measured by the IS (ICC > 0.75 for 9 out of 11 parameters). Moreover, on-field nGRF patterns demonstrated a progressive and significant increase in relation with the running velocity (p < 0.001). This study demonstrated that the IS is a highly valid tool to assess vGRF patterns on a football field. This innovative way to measure vGRF in situ could give new insights to quantify training load and detect neuromuscular fatigue.

Phase-Specific Force and Time Predictors of Standing Long Jump Distance

This study sought to identify potential predictors of standing long jump (SLJ) performance using force-time strategy metrics within the unloading, eccentric yielding, eccentric braking, and concentric phases. Fifteen National Collegiate Athletic Association division 1 male soccer players (19 [1] y, 1.81 [0.94] m, 80.3 [22.4] kg) performed 3 maximum-effort SLJs, while 3-dimensional ground reaction force (GRF) data were obtained. Regularized regression models were used to investigate associations between force-time strategy metrics and 2 metrics of SLJ performance (ie, jump distance and modified reactive strength index). Jump height and eccentric yielding time were the only predictors of jump distance that also demonstrated large correlations to jump distance. Anterior-posterior unloading yank, average concentric vertical force, and concentric phase duration were the only predictors of modified reactive strength index that also demonstrated large correlations to modified reactive strength index. To maximize SLJ distance in high-level soccer athletes, human performance practitioners could design interventions to drive changes in strategy to increase jump height and decrease eccentric yielding time. To improve SLJ explosiveness, interventions to drive changes in unloading and concentric force application and decrease concentric time could be emphasized. Importantly, unique variable combinations can be targeted when training for SLJ distance and explosiveness adaptations.

The effects of mid-flight whole-body and trunk rotation on landing mechanics: implications for anterior cruciate ligament injuries

The purpose was to quantify the effects of mid-flight whole-body and trunk rotation on knee mechanics in a double-leg landing. Eighteen male and 20 female participants completed a jump-landing-jump task in five conditions: no rotation, testing leg ipsilateral or contralateral (WBRC) to the whole-body rotation direction, and testing leg ipsilateral (TRI) or contralateral to the trunk rotation direction. The WBRC and TRI conditions demonstrated decreased knee flexion and increased knee abduction angles at initial contact (2.6 > Cohen's dz > 0.3) and increased peak vertical ground reaction forces and knee adduction moments during the 100 ms after landing (1.7 > Cohen's dz > 0.3). The TRI condition also showed the greatest knee internal rotation angles at initial contact and peak knee abduction and internal rotation angles and peak knee extension moments during the 100 ms after landing (2.0 > Cohen's dz > 0.5). Whole-body rotation increased contralateral knee loading because of its primary role in decelerating medial-lateral velocities. Trunk rotation resulted in the greatest knee loading for the ipsilateral knee due to weight shifting and mechanical coupling between the trunk and lower extremities. These findings may help understand altered trunk motion in anterior cruciate ligament injuries.

Physical Fitness Characteristics of High-level Youth Football Players: Influence of Playing Position

The aim of this study was to determine whether the speed, agility, aerobic and anaerobic capacities of football players varied by playing positions. Elite youth football players (n = 123, age = 15.7 ± 0.5 years) who played in six different positions, as goalkeepers (GK), full backs (FB), central defenders (CD), wide midfielders (WM), central midfielders (CM), and attackers (AT), were assessed. Multivariate analysis of variances was used to compare the following variables: Linear running sprint for 5 m (S5) and 10 m (S10), flying sprint for 20 m (F20), agility 505 test with turn on the dominant (A505D) and non-dominant leg (A505N), agility K-test, Yo-Yo intermittent recovery (YYIR1) test and repeat sprint ability (RSA) test. The results showed significant influence of playing positions on linear-running sprint performance (F1,123 = 6.19, p < 0.01, ηp² = 0.23). Midfielders reached significantly higher performance levels (CM = 2.44 ± 0.08 s, WM = 2.47 ± 0.13 s) in the A505N test compared to GK (2.61 ± 0.23 s). Outfield players had significantly higher performance in both YYIR1 and RSA tests compared to GK (p < 0.01). The results of this study may provide insightful strategies for coaches and clinical practitioners for developing position-specific conditioning programs.

Weighted vest effects on impact forces and joint work during vertical jump landings in men and women

Weighted vest (WV) use during vertical jump landings (VJL) does not appear to alter peak vertical ground reaction forces (GRF) or peak joint torques. However, WV effects on joint work and sex differences during VJL are not well understood. This study assessed WV effects on vertical GRF and sagittal joint work during VJL in men and women. Twelve men and 12 women performed VJL wearing a WV with zero added mass (unloaded) and with 10% body mass (loaded) while GRF and kinematic data were obtained. Mixed-model analyses of variance (α = 0.05) and effect sizes (ES) were used to assess differences between sexes and/or load conditions. Regardless of sex, greater landing height (p < 0.001; ES = 0.37) and peak vertical GRF (p = 0.001; ES 0.51) occurred when unloaded, while greater landing time (p = 0.001; ES = 0.46) and negative lower extremity work (p < 0.001; ES = 0.41) occurred when loaded through greater negative work about the hip (p = 0.001; ES = 0.27) and ankle (p = 0.020; ES = 0.27). No differences in hip (p = 0.753; ES = 0.03), knee (p = 0.588; ES = 0.07), or ankle (p = 0.580; ES = 0.09) joint displacement were detected between loaded and unloaded conditions. Men exhibited greater landing heights (p < 0.001; ES = 2.49) and greater peak vertical GRF than women (p = 0.007; ES = 1.18), though women exhibited greater negative lower extremity work (p < 0.001; ES = 1.98) than men through greater negative knee (p < 0.001; ES = 1.98) and ankle (p = 0.032; ES = 0.94) work. No sex differences were detected for joint angular displacement about the hip (p = 0.475; ES = 0.30), knee (p = 0.666; ES = 0.18), or ankle (p = 0.084; ES = 0.71). These data revealed a unique load accommodation strategy during VJL with a WV characterized by greater lower extremity joint work performed via increased joint torque despite lesser landing height and peak vertical GRF. Women appear to perform greater lower extremity joint work than men during VJL despite lesser landing height and peak vertical GRF. Current and prospective WV users should be aware of their load accommodation strategy during VJL with an external load. Women may consider developing more refined load accommodation strategies for VJL regardless of whether external loading is applied to avoid performing excessive amounts of lower extremity work.

Evaluating Performance During Maximum Effort Vertical Jump Landings

The ability to rapidly complete a jump landing has received little attention in the literature despite the need for rapid performance in a number of sports. As such, our purpose was to investigate differences between groups of individuals who land quickly (FAST) and slowly (SLOW) relative to peak vertical ground reaction forces (vGRFs), loading rates, rates of vGRF attenuation, contributions to lower extremity mechanical energy absorption at the involved joints, and the onsets of preparatory joint flexion/dorsiflexion. Twenty-four healthy adults (26.1 [3.3] y, 75.7 [18.9] kg, 1.7 [0.1] m) were stratified into FAST and SLOW groups based on landing time across 8 jump-landing trials. Independent t tests (α = .05) and effect sizes (ESs; large ≥ 0.8) compared differences between groups. A greater rate of vGRF attenuation (P = .02; ES = 0.95) was detected in the FAST group. The FAST group also exhibited greater contributions to lower extremity energy absorption at the ankle (P = .03; ES = 0.98) and knee (P = .03; ES = 0.99) during loading and attenuation, respectively. The SLOW group exhibited greater contributions to energy absorption at the hip during loading (P = .02; ES = 1.10). Results suggest that individuals who land quickly utilize different energy absorption strategies than individuals who land slowly. Ultimately, the FAST group’s strategy resulted in superior landing performance (more rapid landing time).

Kinetic and Electromyographic Subphase Characteristics With Relation to Countermovement Vertical Jump Performance

This study sought to identify kinetic and electromyographic subphase characteristics distinguishing good from poor jumpers during countermovement vertical jumps (CMVJs), as defined by the reactive strength index (RSI, CMVJ displacement divided by jump time; cutoff = 0.46 m·s−1). A total of 15 men (1.8 [0.6] m, 84.5 [8.5] kg, 24 [2] y) were stratified by RSI into good (n = 6; RSI = 0.57 [0.07] m·s−1) and poor (n = 9; RSI = 0.39 [0.06] m·s−1) performance groups. The following variables were compared between groups using independentttests (α = .05) and Cohen’sdeffect sizes (d ≥ 0.8, large): jump height, propulsive impulse, eccentric rate of force development, and jump time, unloading, eccentric, and concentric subphase times, and average electromyographic amplitudes of 8 lower extremity muscles. Compared with the poor RSI group, the good RSI group exhibited a greater, though not statistically different CMVJ displacement (d = 1.07,P = .06). In addition, the good RSI group exhibited a significantly greater propulsive impulse (P = .04,d = 1.27) and a significantly more rapid unloading subphase (P = .04,d = 1.08). No other significant or noteworthy differences were detected. Enhanced RSI appears related to a quicker unloading phase, allowing a greater portion of the total jumping phase to be utilized generating positive net force. Poor jumpers should aim to use unloading strategies that emphasize quickness to enhance RSI during CMVJ.

Performance Differences Among Skilled Soccer Players of Different Playing Positions During Vertical Jumping and Landing

Harry, JR, Barker, LA, James, CR, and Dufek, JS. Performance differences among skilled soccer players of different playing positions during vertical jumping and landing. J Strength Cond Res 32(2): 304-312, 2018-Both jumping and landing performance of skilled soccer players is diminished when task demands are increased. However, it is unclear if performance changes are specific to players of certain playing positions. Therefore, we assessed jumping and landing performance among skilled soccer players of different playing positions. Twenty-five National Collegiate Athletic Association (NCAA) Division 1 male soccer players (179.5 ± 7.8 cm, 75.5 ± 7.1 kg, 19.7 ± 1.2 years) performed maximum effort vertical jump landings (VJLs), whereas vertical ground reaction force (vGRF) data were obtained. Participants were stratified into goalkeeping (GK), defensive (DEF), midfield (MID), and attacking (ATT) group according to their primary playing position. One-way analyses of variance (α = 0.05) and effect sizes (ESs; large ≥ 0.80) were used to compare differences among groups. The jumping phase variables evaluated were jump height, unloading and amortization vGRF magnitudes, eccentric rate of force development, and the reactive strength index. Landing phase variables included the peak vGRF magnitude, vGRF loading rate, vGRF attenuation rate, and landing time. No statistically significant differences were detected for any jumping or landing variable (p ≥ 0.05). However, a number of large magnitude differences were detected during landing after ES calculations. Specifically, greater peak vGRF magnitudes were detected in DEF vs. both MID (ES = 1.08) and ATT (ES = 0.93), a greater vGRF loading rate occurred in DEF vs. MID (ES = 0.93), and a greater vGRF attenuation rate occurred in DEF vs. both MID (ES = 1.00) and AT (ES = 0.80). It is concluded that highly skilled soccer players possess position-specific abilities with respect to the landing phase of VJL. Skilled soccer players might experience enhanced training outcomes after VJL training regimens tailored to the specific demands of their primary playing position.