1RM prediction: a novel methodology based on the force-velocity and load-velocity relationships.

PURPOSE: This study aimed to evaluate the accuracy of a novel approach for predicting the one-repetition maximum (1RM). The prediction is based on the force-velocity and load-velocity relationships determined from measured force and velocity data collected during resistance-training exercises with incremental submaximal loads. 1RM was determined as the load corresponding to the intersection of these two curves, where the gravitational force exceeds the force that the subject can exert. METHODS: The proposed force-velocity-based method (FVM) was tested on 37 participants (23.9 ± 3.1 year; BMI 23.44 ± 2.45) with no specific resistance-training experience, and the predicted 1RM was compared to that achieved using a direct method (DM) in chest-press (CP) and leg-press (LP) exercises. RESULTS: The mean 1RM in CP was 99.5 kg (±27.0) for DM and 100.8 kg (±27.2) for FVM (SEE = 1.2 kg), whereas the mean 1RM in LP was 249.3 kg (±60.2) for DM and 251.1 kg (±60.3) for FVM (SEE = 2.1 kg). A high correlation was found between the two methods for both CP and LP exercises (0.999, p < 0.001). Good agreement between the two methods emerged from the Bland and Altman plot analysis. CONCLUSION: These findings suggest the use of the proposed methodology as a valid alternative to other indirect approaches for 1RM prediction. The mathematical construct is simply based on the definition of the 1RM, and it is fed with subject's muscle strength capacities measured during a specific exercise. Its reliability is, thus, expected to be not affected by those factors that typically jeopardize regression-based approaches.

Head stabilization in children of both genders during level walking.

Young healthy adults adopt a "head stabilization in space" strategy during walking by attenuating the acceleration going up from pelvis-to-head level. A gender difference exists in this control strategy, particularly evident in the control of medio-lateral dynamic equilibrium. This study aims at assessing whether this difference is already present at pre-pubertal age. Two groups of children (15 females and 15 males, age range: 8-11 years) were involved in the study. They were asked to walk at self-selected speed and movement data were collected using three inertial sensors firmly attached at pelvis (P), shoulder (S), and head (H) levels. The RMS of the accelerations of P, S, and H were computed along the antero-posterior (AP), medio-lateral (ML), and vertical (V) directions and used to compare the two groups. No differences were found between the two groups in the pelvis and shoulder acceleration RMS values. Conversely, lower head acceleration RMS values were found for the females in both the AP and ML directions. Both groups managed to attenuate the upper body AP and ML accelerations going from pelvis-to-head level, with higher attenuations found for the females. The results of this study suggest that the gender differences in the ability to control the head accelerations during gait, found in a previous study, are due neither to different mass distribution nor to a compensation of the greater pelvic motions, nor are they the result of gender related walking habits (e.g. use of high heels).

Assessment of level-walking aperiodicity.

BACKGROUND: In gait analysis, walking is assumed to be periodic for the sake of simplicity, despite the fact that, strictly speaking, it can only approximate periodicity and, as such, may be referred to as pseudo-periodic. This study aims at: 1) quantifying gait pseudo-periodicity using information concerning a single stride; 2) investigating the effects of walking pathway length on gait periodicity; 3) investigating separately the periodicity of the upper and lower body parts movement; 4) verifying the validity of foot-floor contact events as markers of the gait cycle period. METHODS: Ten young healthy subjects (6 males, 23 +/- 5 years) were asked to perform various gait trials, first along a 20-m pathway that allowed reaching a steady-state condition, and then along an 8-m pathway. A stereophotogrammetric system was used to reconstruct the 3D position of reflective markers distributed over the subjects' body. Foot contact was detected using an instrumented mat. Three marker clusters were used to represent the movement of the whole body, the upper body (without upper limbs), and the lower body, respectively. Linear and rotational kinetic, and gravitational and elastic potential "energy-like" quantities were used to calculate an index J(t) that described the instantaneous "mechanical state" of the analysed body portion. The variations of J(t) in time allowed for the determination of the walking pseudo-period and for the assessment of gait aperiodicity. RESULTS: The suitability of the proposed approach was demonstrated, and it was shown that, for young, healthy adults, a threshold of physiological pseudo-periodicity of walking at natural speed could be set. Higher pseudo-periodicity values were found for the shorter pathway only for the upper body. Irrespective of pathway length, the upper body had a larger divergency from periodicity than the lower body. The error that can be made in estimating the gait cycle duration for the upper body from the heel contacts was shown to be significant. CONCLUSION: The proposed method can be easily implemented in gait laboratories to verify the consistency of a recorded stride with the hypothesis of periodicity.

Sequencing sit-to-stand and upright posture for mobility limitation assessment: determination of the timing of the task phases from force platform data.

The identification of quantitative tools to assess an individual's mobility limitation is a complex and challenging task. Several motor tasks have been designated as potential indicators of mobility limitation. In this study, a multiple motor task obtained by sequencing sit-to-stand and upright posture was used. Algorithms based on data obtained exclusively from a single force platform were developed to detect the timing of the motor task phases (sit-to-stand, preparation to the upright posture and upright posture). To test these algorithms, an experimental protocol inducing predictable changes in the acquired signals was designed. Twenty-two young, able-bodied subjects performed the task in four different conditions: self-selected natural and high speed with feet kept together, and self-selected natural and high speed with feet pelvis-width apart. The proposed algorithms effectively detected the timing of the task phases, the duration of which was sensitive to the four different experimental conditions. As expected, the duration of the sit-to-stand was sensitive to the speed of the task and not to the foot position, while the duration of the preparation to the upright posture was sensitive to foot position but not to speed. In addition to providing a simple and effective description of the execution of the motor task, the correct timing of the studied multiple task could facilitate the accurate determination of variables descriptive of the single isolated phases, allowing for a more thorough description of the motor task and therefore could contribute to the development of effective quantitative functional evaluation tests.

Total body centre of mass displacement estimated using ground reactions during transitory motor tasks: application to step ascent.

A double integration technique is presented that estimates whole body centre of mass (CoM) displacement from signals of a single force platform, compensating for the drift and low frequency noise inherent in the signals. The technique is composed of two different integration techniques, which may also be used separately, and is applied to transitory motor tasks with known initial and final conditions such as step ascent and descent, single step, etc. First, the lowest frequencies within the force platform signals and considered not to be associated with actual movement are filtered out. Second, a regular and a time-reversed double integration are performed and weighted against each other. The technique's accuracy was assessed using computer generated force platform signals that were artificially perturbed. Experimental data were used to compare the estimated CoM displacement to that obtained from a regular double integration and from segmental analysis performed on stereophotogrammetric data. It was shown that the proposed technique's CoM displacement estimates were more repeatable and up to 50% more accurate than those of a regular double integration. Moreover, the CoM displacement estimated using a single force platform and the proposed technique was found to be not statistically different from that obtained with more demanding measurement and processing techniques such as stereophotogrammetry and segmental analysis.