to quantify the neuromuscular mechanical capabilities for both testing and training. For the lower limbs, Samozino et al 18 developed a simple method involving classical Newtonian mechanics to evaluate force, velocity, and power output during explosive squat jumps by means of easy-to-measure data
Abderrahmane Rahmani, Pierre Samozino, Jean-Benoit Morin and Baptiste Morel
Pedro Jiménez-Reyes, Pierre Samozino, Fernando Pareja-Blanco, Filipe Conceição, Víctor Cuadrado-Peñafiel, Juan José González-Badillo and Jean-Benoît Morin
To analyze the reliability and validity of a simple computation method to evaluate force (F), velocity (v), and power (P) output during a countermovement jump (CMJ) suitable for use in field conditions and to verify the validity of this computation method to compute the CMJ force–velocity (F–v) profile (including unloaded and loaded jumps) in trained athletes.
Sixteen high-level male sprinters and jumpers performed maximal CMJs under 6 different load conditions (0–87 kg). A force plate sampling at 1000 Hz was used to record vertical ground-reaction force and derive vertical-displacement data during CMJ trials. For each condition, mean F, v, and P of the push-off phase were determined from both force-plate data (reference method) and simple computation measures based on body mass, jump height (from flight time), and push-off distance and used to establish the linear F–v relationship for each individual.
Mean absolute bias values were 0.9% (± 1.6%), 4.7% (± 6.2%), 3.7% (± 4.8%), and 5% (± 6.8%) for F, v, P, and slope of the F–v relationship (SFv), respectively. Both methods showed high correlations for F–v-profile-related variables (r = .985–.991). Finally, all variables computed from the simple method showed high reliability, with ICC >.980 and CV <1.0%.
These results suggest that the simple method presented here is valid and reliable for computing CMJ force, velocity, power, and F–v profiles in athletes and could be used in practice under field conditions when body mass, push-off distance, and jump height are known.
Jean-Benoît Morin, Georges Dalleau, Heikki Kyröläinen, Thibault Jeannin and Alain Belli
The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new “sine-wave” method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function, this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m·s–1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67% to 6.93% less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements.
Tishya A.L. Wren and Paul C. Mitiguy
Clinical gait analysis usually describes joint kinematics using Euler angles, which depend on the sequence of rotation. Studies have shown that pelvic obliquity angles from the traditional tilt-obliquity-rotation (TOR) Euler angle sequence can deviate considerably from clinical expectations and have suggested that a rotation-obliquity-tilt (ROT) Euler angle sequence be used instead. We propose a simple alternate approach in which clinical joint angles are defined and exactly calculated in terms of Euler angles from any rotation sequence. Equations were derived to calculate clinical pelvic elevation, progression, and lean angles from TOR and ROT Euler angles. For the ROT Euler angles, obliquity was exactly the same as the clinical elevation angle, rotation was similar to the clinical progression angle, and tilt was similar to the clinical lean angle. Greater differences were observed for TOR. These results support previous findings that ROT is preferable to TOR for calculating pelvic Euler angles for clinical interpretation. However, we suggest that exact clinical angles can and should be obtained through a few extra calculations as demonstrated in this technical note.
Ming-Lang Tseng, Chien-Chang Ho, Shih-Chang Chen, Yi-Chia Huang, Cheng-Hsiu Lai and Yung-Po Liaw
Evidence suggests that physical activity has a beneficial effect of elevated high-density lipoprotein cholesterol (HDL-C) on reducing coronary artery risk. However, previous studies show contrasting results for this association between different types of exercise training (i.e., aerobic, resistance, or combined aerobic and resistance training). The aim of this study was to determine which type of exercise training is more effective in increasing HDL-C levels. Forty obese men, age 18–29 yr, were randomized into 4 groups: an aerobic-training group (n = 10), a resistance-training group (n = 10), a combined-exercise-training group (n = 10), and a control group (n = 10). After a 12-wk exercise program, anthropometrics, blood biochemical variables, and physical-fitness components were compared with the data obtained at the baseline. Multiple-regression analysis was used to evaluate the association between different types of exercise training and changes in HDL-C while adjusting for potential confounders. The results showed that with the control group as the comparator, the effects of combined-exercise training (β = 4.17, p < .0001), aerobic training (β = 3.65, p < .0001), and resistance training (β = 2.10, p = .0001) were positively associated with increase in HDL-C after adjusting for potential confounders. Our findings suggested that a short-term exercise program can play an important role in increasing HDL-C levels; either aerobic or resistance training alone significantly increases the HDL-C levels, but the improvements are greatest with combined aerobic and resistance training.
Caroline Giroux, Giuseppe Rabita, Didier Chollet and Gaël Guilhem
Performance during human movements is highly related to force and velocity muscle capacities. Those capacities are highly developed in elite athletes practicing power-oriented sports. However, it is still unclear whether the balance between their force and velocity-generating capacities constitutes an optimal profile. In this study, we aimed to determine the effect of elite sport background on the force–velocity relationship in the squat jump, and evaluate the level of optimization of these profiles. Ninetyfive elite athletes in cycling, fencing, taekwondo, and athletic sprinting, and 15 control participants performed squat jumps in 7 loading conditions (range: 0%–60% of the maximal load they were able to lift). Theoretical maximal power (Pm), force (F 0), and velocity (v 0) were determined from the individual force–velocity relationships. Optimal profiles were assessed by calculating the optimal force (F 0th) and velocity (v 0th). Athletic sprinters and cyclists produced greater force than the other groups (P < .05). F 0 was significantly lower than F 0th, and v 0 was significantly higher than v 0th for female fencers and control participants, and for male athletics sprinters, fencers, and taekwondo practitioners (P < .05). Our study shows that the chronic practice of an activity leads to differently balanced force–velocity profiles. Moreover, the differences between measured and optimal force–velocity profiles raise potential sources of performance improvement in elite athletes.
Jo Welsman and Neil Armstrong
In this paper, we draw on cross-sectional, treadmill-determined, peak oxygen uptake data, collected in our laboratory over a 20-year period, to examine whether traditional per body mass (ratio) scaling appropriately controls for body size differences in youth. From an examination of the work of pioneering scientists and the earliest studies of peak oxygen uptake, we show how ratio scaling appears to have no sound scientific or statistical rationale. Using simple methods based on correlation and regression, we demonstrate that the statistical relationships, which are assumed in ratio scaling, are not met in groups of similar aged young people. We also demonstrate how sample size and composition can influence relationships between body mass and peak oxygen uptake and show that mass exponents derived from log-linear regression effectively remove the effect of body mass. Indiscriminate use of ratio scaling to interpret young people’s fitness, to raise “Clinical Red Flags”, and to assess clinical populations concerns us greatly, as recommendations and conclusions based upon this method are likely to be spurious. We urge those involved with investigating youth fitness to reconsider how data are routinely scaled for body size.
Richard Cooke, Helena Trebaczyk, Peter Harris and Alison J. Wright
The present study tests whether a self-affirmation intervention (i.e., requiring an individual to focus on a valued aspect of their self-concept, such as honesty) can increase physical activity and change theory of planned behavior (TPB) variables linked to physical activity. Eighty young people completed a longitudinal intervention study. Baseline physical activity was assessed using the Godin Leisure-Time Physical Activity Questionnaire (LTPAQ). Next, participants were randomly allocated to either a self-affirmation or a nonaffirmation condition. Participants then read information about physical activity and health, and completed measures of TPB variables. One week later, participants again completed LTPAQ and TPB items. At follow up, self-affirmed participants reported significantly more physical activity, more positive attitudes toward physical activity, and higher intentions to be physically active compared with nonaffirmed participants. Neither attitudes nor intentions mediated the effects of self-affirmation on physical activity. Self-affirmation can increase levels of physical activity and TPB variables. Self-affirmation interventions have the potential to become relatively simple methods for increasing physical activity levels.
Alejandro Pérez-Castilla, Belén Feriche, Slobodan Jaric, Paulino Padial and Amador García-Ramos
.1119/1.1397460 4. Samozino P , Morin JB , Hintzy F , Belli A . A simple method for measuring force, velocity and power output during squat jump . J Biomech . 2008 ; 41 ( 14 ): 2940 – 2945 . PubMed doi:10.1016/j.jbiomech.2008.07.028 18789803 10.1016/j.jbiomech.2008
Carlos Balsalobre-Fernández, Hovannes Agopyan and Jean-Benoit Morin
stiffness devices: implications for practical use . J Appl Biomech . 2016 ; 32 ( 4 ): 415 – 419 . PubMed doi: 10.1123/jab.2015-0297 26959196 17. Morin JB , Dalleau G , Kyröläinen H , Jeannin T , Belli A . A simple method for measuring stiffness during running . J Appl Biomech . 2005