We compared running mechanics parameters determined from ground reaction force (GRF) measurements with estimated forces obtained from double differentiation of kinematic (K) data from motion analysis in a broad spectrum of running speeds (1.94–5.56 m⋅s–1). Data were collected through a force-instrumented treadmill and compared at different sampling frequencies (900 and 300 Hz for GRF, 300 and 100 Hz for K). Vertical force peak, shape, and impulse were similar between K methods and GRF. Contact time, flight time, and vertical stiffness (kvert) obtained from K showed the same trend as GRF with differences < 5%, whereas leg stiffness (kleg) was not correctly computed by kinematics. The results revealed that the main vertical GRF parameters can be computed by the double differentiation of the body center of mass properly calculated by motion analysis. The present model provides an alternative accessible method for determining temporal and kinetic parameters of running without an instrumented treadmill.
Gaspare Pavei, Elena Seminati, Jorge L.L. Storniolo and Leonardo A. Peyré-Tartaruga
Kathleen Williams, Kathleen Haywood and Ann VanSant
Older adults threw tennis balls for force and accuracy to examine their adaptability to different task demands. Twenty-one (13 women, 8 men) participants were videotaped as they performed five force and five accuracy throws. The developmental level of each throw was determined; resultant ball velocities also were examined. Roberton’s (1977, 1978) movement components were used in the former analysis. The typical pattern of gender differences occurred for both movement component and velocity measures. Men performed at higher levels than women. Only minor force versus accuracy differences were found in the movement patterns used by either men or women; none of these differences were significant. Clear task differences occurred for ball velocities. Men’s forceful throws were faster than those for accuracy; women’s throws did not differ for the two tasks. The generally lower developmental level of women’s throws accounted for gender differences in velocity. Insufficient task differences may explain the lack of clear contrast in movement patterns.
Simon Avrillon, Boris Jidovtseff, François Hug and Gaël Guilhem
Muscle strengthening is commonly based on the use of isoinertial loading, whereas variable resistances such as pneumatic loading may be implemented to optimize training stimulus. The purpose of the current study was to determine the effect of the ratio between pneumatic and isoinertial resistance on the force–velocity relationship during ballistic movements.
A total of 15 participants performed 2 concentric repetitions of ballistic bench-press movements with intention to throw the bar at 30%, 45%, 60%, 75%, and 90% of the maximal concentric repetition with 5 resistance ratios including 100%, 75%, 50%, 25%, or 0% of pneumatic resistance, the additional load being isoinertial. Force-, velocity-, and power-time patterns were assessed and averaged over the concentric phase to determine the force–velocity and power–velocity relationships for each resistance ratio.
Each 25% increase in the pneumatic part in the resistance ratio elicited higher movement velocity (+0.11 ± 0.03 m/s from 0% to 80% of the concentric phase) associated with lower force levels (–43.6 ± 15.2 N). Increased isoinertial part in the resistance ratio resulted in higher velocity toward the end of the movement (+0.23 ± 0.01 m/s from 90% to 100%).
The findings show that the resistance ratio could be modulated to develop the acceleration phase and force toward the end of the concentric phase (pneumatic-oriented resistance). Inversely, isoinertial-oriented resistance should be used to develop maximal force and maximal power. Resistance modality could, therefore, be considered an innovative variable to modulate the training stimulus according to athletic purposes.
Peter F. Vint and Richard N. Hinrichs
Isometric knee extension force and average integrated EMG of the vastus lateralis muscle were obtained from 27 healthy subjects using a maximum effort, ramp and hold protocol. In each of the 125 total trials mat were included in the analysis, a 2-s plateau region was extracted and divided into two adjacent 1000-ms bins. Variability and reliability of bin-to-bin measurements of force and EMG were then evaluated across 14 different integration intervals ranging from 10 to 1000 ms. Statistical analyses of bin-to-bin variability measures demonstrated that integration intervals of 250 ms and longer significantly reduced variability and improved reliability of average integrated EMG values during maximum effort isometric exertions. Bin-to-bin EMG reliability increased from .728 at 10 ms to .991 at 1000 ms. Force parameters appeared less sensitive to changes in length of the integration interval. It was suggested that longer intervals might also improve the validity of the EMG-force relationship during maximum effort isometric exertions by reducing problems associated with electromechanical delay.
Jean-Benoît Morin and Pierre Samozino
Recent studies have brought new insights into the evaluation of power-force-velocity profiles in both ballistic push-offs (eg, jumps) and sprint movements. These are major physical components of performance in many sports, and the methods the authors developed and validated are based on data that are now rather simple to obtain in field conditions (eg, body mass, jump height, sprint times, or velocity). The promising aspect of these approaches is that they allow for more individualized and accurate evaluation, monitoring, and training practices, the success of which is highly dependent on the correct collection, generation, and interpretation of athletes’ mechanical outputs. The authors therefore wanted to provide a practical vade mecum to sports practitioners interested in implementing these power-force-velocity–profiling approaches. After providing a summary of theoretical and practical definitions for the main variables, the authors first detail how vertical profiling can be used to manage ballistic push-off performance, with emphasis on the concept of optimal force–velocity profile and the associated force–velocity imbalance. Furthermore, they discuss these same concepts with regard to horizontal profiling in the management of sprinting performance. These sections are illustrated by typical examples from the authors’ practice. Finally, they provide a practical and operational synthesis and outline future challenges that will help further develop these approaches.
AmirAli Jafarnezhadgero, Morteza Madadi-Shad, Christopher McCrum and Kiros Karamanidis
Human lower limbs contribute to locomotion in multiple ways; acting as springs, as force absorbing dampers, or as actuators ( Brown, O’Donovan, Hasselquist, Corner, & Schiffman, 2016 ; Raynor, Yi, Abernethy, & Jong, 2002 ). The progression of ground reaction forces (GRF) through the lower limbs
Saira Chaudhry, Dylan Morrissey, Roger C. Woledge, Dan L. Bader and Hazel R.C. Screen
Triceps surae eccentric exercise is more effective than concentric exercise for treating Achilles tendinopathy, however the mechanisms underpinning these effects are unclear. This study compared the biomechanical characteristics of eccentric and concentric exercises to identify differences in the tendon load response. Eleven healthy volunteers performed eccentric and concentric exercises on a force plate, with ultrasonography, motion tracking, and EMG applied to measure Achilles tendon force, lower limb movement, and leg muscle activation. Tendon length was ultrasonographically tracked and quantified using a novel algorithm. The Fourier transform of the ground reaction force was also calculated to investigate for tremor, or perturbations. Tendon stiffness and extension did not vary between exercise types (P = .43). However, tendon perturbations were significantly higher during eccentric than concentric exercises (25%–40% higher, P = .02). Furthermore, perturbations during eccentric exercises were found to be negatively correlated with the tendon stiffness (R 2 = .59). The particular efficacy of eccentric exercise does not appear to result from variation in tendon stiffness or extension within a given session. However, varied perturbation magnitude may have a role in mediating the observed clinical effects. This property is subject-specific, with the source and clinical timecourse of such perturbations requiring further research.
Matt S. Stock and Brennan J. Thompson
We examined the means, medians, and variability for motor-unit interpulse intervals (IPIs) during voluntary, high force contractions. Eight men (mean age = 22 years) attempted to perform isometric contractions at 90% of their maximal voluntary contraction force while bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and vastus medialis muscles. Surface EMG signal decomposition was used to determine the recruitment thresholds and IPIs of motor units that demonstrated accuracy levels ≥ 96.0%. Motor units with high recruitment thresholds demonstrated longer mean IPIs, but the coefficients of variation were similar across all recruitment thresholds. Polynomial regression analyses indicated that for both muscles, the relationship between the means and standard deviations of the IPIs was linear. The majority of IPI histograms were positively skewed. Although low-threshold motor units were associated with shorter IPIs, the variability among motor units with differing recruitment thresholds was comparable.
Matthew Brodie, Alan Walmsley and Wyatt Page
A fusion integration algorithm is used to estimate the one-dimensional center of mass (COM) trajectory from force platform data. The resulting COM trajectory combines the best attributes of several established algorithms used to estimate the COM trajectory, and it appears to have the advantage of being robust, accurate, continuous in its higher derivatives, and fast to obtain. In current research projects, variations of the fusion integration algorithm have been adapted by the authors for the analysis of postural balance and the sensing of limb orientations with inertial measurement units.
Philip E. Martin and Gary D. Heise
Archery instructors believe that force distribution (FD) between the hand and bow grip can have a considerable effect on arrow flight, but there is no empirical support for this speculation. This study examined FD on the bow grip in experienced archers and explored the possible relationships between FD, performance, and fatigue. FD was quantified for 15 experienced archers (8 highly skilled [HS] and 7 less skilled [LS]) using 15 unobtrusive force sensors as each archer completed 72 shots. Arrow position relative to the target center, estimated net moments and moment arms about vertical and horizontal axes through the grip, and shot-to-shot variability in the estimated moments and moment arms were computed for three blocks of six shots. Results demonstrated that (a) estimated moments and moment arms were not consistently related to observed vertical or horizontal deviations in arrow position, (b) there were no systematic differences in FD between HS and LS archers, (c) fatigue had no quantifiable effect on FD, and (d) HS archers displayed less shot-to-shot variability in vertical FD than LS archers, but similar variability horizontally. Results did not support the above-noted common belief of archery instructors.