Measuring the ground reaction forces (GRF) underlying sprint acceleration is important to understanding the performance of such a common task. Until recently direct measurements of GRF during ...sprinting were limited to a few steps per trial, but a simple method (SM) was developed to estimate GRF across an entire acceleration. The SM utilizes displacement- or velocity-time data and basic computations applied to the runner’s center of mass and was validated against compiled force plate (FP) measurements; however, this validation used multiple-trials to generate a single acceleration profile, and consequently fatigue and error may have introduced noise into the analyses. In this study, we replicated the original validation by comparing the main sprint kinetics and force-velocity-power variables (e.g. GRF and its horizontal and vertical components, mechanical power output, ratio of horizontal component to resultant GRF) between synchronized FP data from a single sprinting acceleration and SM data derived from running velocity measured with a 100 Hz laser. These analyses were made possible thanks to a newly developed 50-m FP system providing seamless GRF data during a single sprint acceleration. Sixteen trained male sprinters performed two all-out 60-m sprints. We observed good agreement between the two methods for kinetic variables (e.g. grand average bias of 4.71%, range 0.696 ± 0.540–8.26 ± 5.51%), and high inter-trial reliability (grand average standard error of measurement of 2.50% for FP and 2.36% for the SM). This replication study clearly shows that when implemented correctly, this method accurately estimates sprint acceleration kinetics.
In the last years, gait phase partitioning has come to be a challenging research topic due to its impact on several applications related to gait technologies. A variety of sensors can be used to feed ...algorithms for gait phase partitioning, mainly classifiable as wearable or non-wearable. Among wearable sensors, footswitches or foot pressure insoles are generally considered as the gold standard; however, to overcome some inherent limitations of the former, inertial measurement units have become popular in recent decades. Valuable results have been achieved also though electromyography, electroneurography, and ultrasonic sensors. Non-wearable sensors, such as opto-electronic systems along with force platforms, remain the most accurate system to perform gait analysis in an indoor environment. In the present paper we identify, select, and categorize the available methodologies for gait phase detection, analyzing advantages and disadvantages of each solution. Finally, we comparatively examine the obtainable gait phase granularities, the usable computational methodologies and the optimal sensor placements on the targeted body segments.
•The Wii Balance Board has been increasingly used for balance assessment.•Research has demonstrated variable results when compared with other force platforms.•This review supports the reliability and ...concurrent validity of the Wii Balance Board.•However, the methodology for data acquisition will impact on performance.
The use of force platform technologies to assess standing balance is common across a range of clinical areas. Numerous researchers have evaluated the low-cost Wii Balance Board (WBB) for its utility in assessing balance, with variable findings. This review aimed to systematically evaluate the reliability and concurrent validity of the WBB for assessment of static standing balance. Articles were retrieved from six databases (Medline, SCOPUS, EMBASE, CINAHL, Web of Science, Inspec) from 2007 to 2017. After independent screening by two reviewers, 25 articles were included. Two reviewers performed the data extraction and quality assessment. Test-retest reliability was investigated in 12 studies, with intraclass correlation coefficients or Pearson’s correlation values showing a range from poor to excellent reliability (range: 0.27 to 0.99). Concurrent validity (i.e. comparison with another force platform) was examined in 21 studies, and was generally found to be excellent in studies examining the association between the same outcome measures collected on both devices. For studies reporting predominantly poor to moderate validity, potentially influential factors included the choice of 1) criterion reference (e.g. not a common force platform), 2) test duration (e.g. <30 s for double leg), 3) outcome measure (e.g. comparing a centre of pressure variable from the WBB with a summary score from the force platform), 4) data acquisition platform (studies using Apple iOS reported predominantly moderate validity), and 5) low sample size. In conclusion, evidence suggests that the WBB can be used as a reliable and valid tool for assessing standing balance.
Protocol registration number: PROSPERO 2017: CRD42017058122.
Several statements on the still debated issue of stabilometry standardization were agreed upon by the ISPGR Standardization Committee. * A set of metrological characteristics for stabilometric ...platforms was defined. * Relying both on practice and experimental verification it was agreed that, to obtain appropriate accuracy and sensitivity in the Romberg Test: * The acquisition interval should not be less than 25 s. * The sampling frequency should be at least 50 Hz. * After careful consideration it was decided that the recommendations made in the previous Standardization proposal in 1983 regarding environmental conditions should be maintained.
This study aimed to compare the load-velocity and load-power relationships of three common variations of the squat exercise. 52 strength-trained males performed a progressive loading test up to the ...one-repetition maximum (1RM) in the full (F-SQ), parallel (P-SQ) and half (H-SQ) squat, conducted in random order on separate days. Bar velocity and vertical force were measured by means of a linear velocity transducer time-synchronized with a force platform. The relative load that maximized power output (Pmax) was analyzed using three outcome measures: mean concentric (MP), mean propulsive (MPP) and peak power (PP), while also including or excluding body mass in force calculations. 1RM was significantly different between exercises. Load-velocity and load-power relationships were significantly different between the F-SQ, P-SQ and H-SQ variations. Close relationships (R
2
= 0.92-0.96) between load (%1RM) and bar velocity were found and they were specific for each squat variation, with faster velocities the greater the squat depth. Unlike the F-SQ and P-SQ, no sticking region was observed for the H-SQ when lifting high loads. The Pmax corresponded to a broad load range and was greatly influenced by how force output is calculated (including or excluding body mass) as well as the exact outcome variable used (MP, MPP, PP).
This study aimed to investigate the effect of countermovement depth on the magnitude of the countermovement jump (CMJ) derived reactive strength index modified (RSI
mod
), and to compare the RSI
mod
...between the CMJ performed with a self-preferred knee flexion angle (CMJ
pref
) and the CMJ performed from a pre-determined knee flexion angle (CMJ
refer
) with the countermovement depth more similar to the CMJ
pref
. Sixteen subjects (11 males and 5 females; age 25.1 ± 6.3 years, body mass 69.7 ± 10.2 kg, body height 172.9 ± 8.1 m) randomly performed in a single session the CMJ
pref
and CMJs from five pre-determined knee flexion angles (60°, 75°, 90°, 105°, and 120°). Our results showed that lower knee flexion angles were generally associated with greater RSI
mod
values with the CMJ performed at 60° showing the greatest RSI
mod
(P ≤ 0.049; effect size ES range = 0.19-0.63). The greatest RSI
mod
for the CMJ performed at 60° was caused by the proportionally lower values of the time to take-off (ES range = 0.65-1.91) compared to the decrease observed in jump height (ES range = 0.11-0.25). The RSI
mod
was higher for the CMJ
pref
compared to the CMJ
refer
(P < 0.001; ES = 0.34) due to a higher jump height (P = 0.021; ES = 0.14) and reduced time to take-off (P < 0.001; ES = 0.85). These results indicate that practitioners should be careful when interpreting an individual's changes in RSI
mod
when the countermovement depth is not similar across the testing sessions. However, since the use of pre-determined knee flexion angles negatively impacts the RSI
mod
, we encourage practitioners to use the CMJ
pref
but only compare the RSI
mod
when CMJs are performed using consistent countermovement depths.
ABSTRACTMcMahon, JJ, Jones, PA, and Comfort, P. Comparison of countermovement jump–derived reactive strength index modified and underpinning force-time variables between super league and championship ...rugby league players. J Strength Cond Res XX(X)000–000, 2019—The countermovement jump (CMJ) is regularly tested in rugby league (RL), with recent work reporting reactive strength index modified (RSImod) to distinguish between levels of play. Differences in CMJ-derived RSImod and underpinning force-time variables between English Super League (SL) and RL Championship (RLC) players are, however, unknown. As SL and RLC teams compete against each other, this study addressed this knowledge gap. Sixty RL players from the English SL (n = 30) and RLC (n = 30) performed 3 CMJs on a force platform at the start of the preseason training. The RSImod was calculated by dividing jump height (JH) by time to take-off (TTT), and several other variables were also extracted from the force-time record. The SL players achieved a significantly higher (large effect) RSImod by performing the CMJ with a significantly shorter (large effect) TTT but a similar (small effect) JH. The SL players achieved the shorter TTT through a significantly reduced (large effects) relative displacement during both the countermovement (combined unweighting and braking displacement) and propulsion phases but a significantly higher (moderate effects) propulsion peak force and power. The relationships between TTT and relative countermovement (r = 0.719, p < 0.001) and propulsion (r = 0.771, p < 0.001) displacement for combined group data were very large. Practitioners working in RL should, therefore, consider reporting RSImod and TTT, alongside JH, after CMJ force-time testing. We also suggest that RL players who produce lower RSImod scores would benefit from being trained to produce larger CMJ propulsion forces over a shallower range of hip, knee, and ankle extension.
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.
This study explores the sensitivity of jump type (unilateral and bilateral) and output variable (mean force, propulsive impulse, and jump height) to detect the changes in inter-limb asymmetries ...induced by unilateral and bilateral fatigue protocols. Thirty-eight individuals performed two testing sessions that consisted of (I) nine "pre-fatigued" countermovement jumps (CMJs; three bilateral and six unilateral three with each leg), (II) fatigue protocol and (III) nine "post-fatigued" CMJs. The testing sessions only differed in the fatigue protocol (five sets to failure against the 15-repetition maximum load using either the unilateral or bilateral knee extension exercise). The magnitude of all CMJ-derived variables (mean force, impulse, and jump height) decreased following both unilateral (p ≤ 0.002) and bilateral fatigue protocols (p ≤ 0.018). However, only unilateral protocol accentuated inter-limb asymmetries, which was detected for all variables during the unilateral CMJ (from −4.33% to −2.04%; all p < 0.05) but not during the bilateral CMJ (from −0.64% to 0.54%; all p > 0.05). The changes in inter-limb asymmetries following the unilateral and bilateral fatigue protocols were not significantly correlated between the unilateral and bilateral CMJs (r
s
≤ 0.172). The unilateral CMJ should be recommended for the testing purposes over the bilateral CMJ due to its greater sensitivity to detect the selective effects of fatigue.
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