Pascale Chavet

Influence of short-term unweighing and reloading on running kinetics and muscle activity

PurposeIn running, body weight reduction is reported to result in decreased lower limb muscle activity with no change in the global activation pattern (Liebenberg et al. in J Sports Sci 29:207–214). Our study examined the acute effects on running mechanics and lower limb muscle activity of short-term unweighing and reloading conditions while running on a treadmill with a lower body positive pressure (LBPP) device.MethodEleven healthy males performed two randomized running series of 9xa0min at preferred speed. Each series included three successive running conditions of 3xa0min [at 100xa0% body weight (BW), 60 or 80xa0% BW, and 100xa0% BW]. Vertical ground reaction force and center of mass accelerations were analyzed together with surface EMG activity recorded from six major muscles of the left lower limb for the first and last 30xa0s of each running condition. Effort sensation and mean heart rate were also recorded.ResultIn both running series, the unloaded running pattern was characterized by a lower step frequency (due to increased flight time with no change in contact time), lower impact and active force peaks, and also by reduced loading rate and push-off impulse. Amplitude of muscle activity overall decreased, but pre-contact and braking phase extensor muscle activity did not change, whereas it was reduced during the subsequent push-off phase.ConclusionThe combined neuro-mechanical changes suggest that LBPP technology provides runners with an efficient support during the stride. The after-effects recorded after reloading highlight the fact that 3xa0min of unweighing may be sufficient for updating the running pattern.

Influence of Muscle Preactivation of the Lower Limb on Impact Dynamics in the Case of Frontal Collision

Abstract Accidentology or shock biomechanics are research domains mainly devoted to the development of safety conditions for the users of various transport modes in the case of an accident. The objective of this study was to improve the knowledge of the biomechanical behaviour of the lower limb facing sudden dynamic loading during a frontal collision. We aimed at establishing the relationship between the level of muscular activity prior to impact, called ‘preactivation’, of the lower-limb extensors and the mechanical characteristics of impact. Relationships were described between the level of preactivation, the impact peak force values, the minimum force after unloading and the associated loading and unloading rates. The existence of reflex mechanisms that were affected by the level of voluntary muscular preactivation for the lower-limb muscles was demonstrated. In conclusion, the existence of a specific mechanism acting mainly at the knee level may result from the level of preactivation. Muscle behaviour has to be included in numerical models of the human driver to better evaluate the overall stiffness of the body before and at impact.

The influence of shoe drop on the kinematics and kinetics of children tennis players

Abstract This study investigated the immediate effects of reducing the shoe drop (i.e. the difference between the heel and the forefoot height) on the kinematics and kinetics of the lower extremities of children tennis players performing a tennis-specific movement. Thirteen children tennis players performed a series of simulated open stance forehands wearing 3 pairs of shoes differing only in the drop: 0 (D0), 6 (D6) and the control condition of 12u2005mm (D12). Two embedded forceplates and a motion capture system were used to analyse the ground reaction forces and ankle and knee joint angles and moments of the leading lower limb. In D6 compared with D12, the peak impact force was reduced by 24% (pu2009=u2009.004) and the ankle was less dorsiflexed at foot strike (pu2009=u2009.037). In D0 compared with D12, the peak impact force was reduced by 17% (pu2009=u2009.049), the ankle was less dorsiflexed at foot strike (pu2009=u2009.045) and the knee was more flexed at foot strike (pu2009=u2009.007). In addition, 4 out of 13 participants (31%) presented a forefoot strike pattern for some of the trials in D0. No difference was observed across shoe conditions for the peak knee extensor moment (pu2009=u2009.658) or the peak ankle plantarflexor moment (pu2009=u2009.071). The results provide preliminary data supporting the hypothesis that for children tennis players, using a 6-mm lower shoe drop might reduce heel impact forces and thus limit potentially impact-related injuries.

Lower shoe drop can reduce impact forces experienced by junior tennis players performing an open-stance forehand

Lower shoe drop can reduce impact forces experienced by junior tennis players performing an open-stance forehand Alexis Herbaut, Emilie Simoneau, Franck Barbier, Maxime Roux, Nils Gueguen & Pascale Chavet a Movement Sciences Department, Decathlon, Villeneuve dAscq, France b Universite de Valenciennes, Valenciennes, France c Aix-Marseille Universite, Marseille, France Published online: 18 Jun 2015.

The influence of shoe aging on children running biomechanics

Athletic children are prone to overuse injuries, especially at the heel and knee. Since footwear is an extrinsic factor of lower limb injury risk, the aim of this study was to assess the influence of shoe aging on children running biomechanics. Fourteen children active in sports participated in a laboratory biomechanical evaluation. A new pair of shoes was provided to each participant at an inclusion visit. Four months later, the participants performed a running task and their kinematics and kinetics were assessed both with their used shoes and with a new pair of shoes identical to the first. Furthermore, mechanical cushioning properties of shoes were evaluated before and after in-vivo aging. After 4months of use, the sole stiffness increased by 16% and the energy loss capacity decreased by 18% (p<0.001). No ankle or knee kinematic adjustment was found at foot strike in used shoes but changes were observed later during stance. Running with used shoes produced a higher loading rate of the vertical ground reaction force (+23%, p=0.016), suggesting higher compressive forces under the heel and placing children at risk to experience impact-related injuries. Nevertheless, the decreased peak ankle and knee power absorption in used shoes (-11%, p=0.010 and -12%, p=0.029, respectively) suggests a lower ankle and knee joints loading during the absorption phase that may be beneficial regarding stretch-related injuries.

Plantar Sole Unweighting Alters the Sensory Transmission to the Cortical Areas

It is well established that somatosensory inputs to the cortex undergo an early and a later stage of processing. The later has been shown to be enhanced when the earlier transmission decreased. In this framework, mechanical factors such as the mechanical stress to which sensors are subjected when wearing a loaded vest are associated with a decrease in sensory transmission. This decrease is in turn associated with an increase in the late sensory processes originating from cortical areas. We hypothesized that unweighting the plantar sole should lead to a facilitation of the sensory transmission. To test this hypothesis, we recorded cortical somatosensory evoked potentials (SEPs) of individuals following cutaneous stimulation (by mean of an electrical stimulation of the foot sole) in different conditions of unweighting when standing still with eyes closed. To this end, the effective bodyweight (BW) was reduced from 100% BW to 40% BW. Contrary to what was expected, we found an attenuation of sensory information when the BW was unweighted to 41% which was not compensated by an increase of the late SEP component. Overall these results suggested that the attenuation of sensory transmission observed in 40 BW condition was not solely due to the absence of forces acting on the sole of the feet but rather to the current relevance of the afferent signals related to the balance constraints of the task.

Neuro-mechanical adjustments to shod versus barefoot treadmill runs in the acute and delayed stretch-shortening cycle recovery phases

Abstract In habitually shod recreational runners, we studied the combined influence of footwear and stretch-shortening cycle (SSC) fatigue on treadmill running pattern, paying special attention to neuro-mechanical adjustments in the acute and 2-day delayed recovery periods. The SSC exercise consisted of a series of 25 sub-maximal rebounds on a sledge apparatus repeated until exhaustion. The acute and delayed functional fatigue effects were quantified in a maximal drop jump test. The neuro-mechanical adjustments to fatigue were examined during two submaximal treadmill run tests of 3 min performed either barefoot or with shoes on. Surface electromyographic (EMG) activities, tibial accelerations and kinematics of the right lower limb were recorded during the first and last 15 s of each run. The main result was that neuro-mechanical differences between the shod and barefoot running patterns, classically reported in the absence of fatigue, persisted in the fatigued state. However, in the delayed recovery phase, rearfoot eversion was found to significantly increase in the shod condition. This specific footwear effect is considered as a potential risk factor of overuse injuries in longer runs. Therefore, specific care should be addressed in the delayed recovery phase of SSC fatigue and the use of motion control shoes could be of interest.

Long-term effects of gradual shoe drop reduction on young tennis players’ kinematics

one-dimensional biomechanical trajectory analysis. Journal of Biomechanics, 48(7), 1277–1285. Roy, J-P.R., & Stefanyshyn, D.J. (2006). Shoe midsole longitudinal bending stiffness and running economy, joint energy, and EMG. Medicine and Science in Sports and Exercise, 38 (3), 562–569. Worobets, J., Tomaras, E., & Stefanyshyn, D. (2014). Softer and more resilient running shoe cushioning properties enhance running economy. Footwear Science, 6(3), 147–153.

Shoe drop reduction influences the lower limb biomechanics of children tennis players during an open stance forehand: A longitudinal study

Abstract Compared to traditional tennis shoes, using 0-drop shoes was shown to induce an immediate switch from rear- to forefoot strike pattern to perform an open stance tennis forehand for 30% of children tennis players. The purpose of the study was to examine the long-term effects of a gradual reduction in the shoe drop on the biomechanics of children tennis players performing open stance forehands. Thirty children tennis players participated in 2 laboratory biomechanical test sessions (intermediate: +4 months and final: +8 months) after an inclusion visit where they were randomly assigned to control (CON) or experimental (EXP) group. CON received 12-mm-drop shoes twice, whereas EXP received 8u2005mm then 4-mm-drop shoes. Strike index indicated that all CON were rearfoot strikers in intermediate and final test sessions. All EXP were rearfoot strikers in intermediate test session, but half the group switched towards a forefoot strike pattern in final test session. This switch resulted in a decreased loading rate of the ground reaction force (−73%, pu2009=u2009.005) but increased peak ankle plantarflexors moment (+47%, pu2009=u2009.050) and peak ankle power absorption (+107%, pu2009=u2009.005) for these participants compared with CON. Biomechanical changes associated with the long-term use of partial minimalist shoes suggest a reduction in heel compressive forces but an increase in Achilles tendon tensile forces.

Determination of optimal shoe fitting for children tennis players: Effects of inner-shoe volume and upper stiffness

The purpose of this study was to determine the optimal inner-shoe volume for children tennis players. Sixteen participants, aged from 8 to 12 years old assessed comfort of 6 shoes, which were a combination of 3 lasts (thin, medium and wide) and 2 upper constructions (flexible and stiff), while a sock equipped with textile sensors was measuring the pressure applied on their foot. The thin last was based on the proportion of an adult last. The widest shoes produced the lowest pressure on the 1st and 5th metatarsal heads, the medial midfoot and the medial and lateral heel (pxa0<xa00.05), whilst they were perceived the most comfortable for the 3rd and 5th metatarsal heads, the 5th metatarsal base and the medial and lateral heel (pxa0<xa00.05). These outcomes indicated that footwear manufacturers should design wider shoes for children than for adults.