Viscoelastic stress relaxation in the hamstrings before and after a 10-week stretching program.

INTRODUCTION: We investigated the viscoelastic stress relaxation response before and after a 10-week hamstrings static stretch program. METHODS: The maximal range of motion (ROMmax ) and maximal torque (Torquemax ) were assessed before and after a 10-week stretching program. Six 30-s static stretches at a predetermined torque were performed, and the relative change in stress relaxation was examined. RESULTS: ROMmax and Torquemax increased by 53% and 82%, respectively (P < 0.001). The relative stress relaxation (RSR) decreased significantly for repetition 1 when comparing the pretest (25%) and posttest (21%) values (P = 0.003). A significant decrease was also observed for repetitions 2 and 3 (P < 0.014), with no significant difference in repetitions 4-6 (P > 0.056). CONCLUSIONS: Individuals who participated in a 10-week hamstrings passive-static stretch program had a reduced RSR response. A higher stretch intensity or longer duration may be necessary to achieve RSRs similar to those reported before the stretch program.

Forefoot midsole stiffness affects forefoot and rearfoot kinematics during the stance phase of gait.

BACKGROUND: The forefoot midsole stiffness of the shoe may affect the kinematics of the foot segments. We evaluated the effects of two different levels of forefoot midsole stiffness on the angular displacement of the forefoot and rearfoot in the three planes of motion during the stance phase of gait. METHODS: Thirty-six participants walked on a 10-m walkway at their self-selected speed wearing shoes having either low or high forefoot midsole stiffness. Three-dimensional kinematic data of the foot segments were obtained during the stance phase of gait using an eight-camera motion analysis system synchronized with a force platform. The dependent variables were forefoot and rearfoot total range of motion and maximum and minimum angle values in the sagittal, frontal, and transverse planes of motion. RESULTS: Reduced forefoot midsole stiffness produced significantly greater forefoot total range of motion in the sagittal plane (1.59°). The low-stiffness condition also increased the magnitude of the forefoot dorsiflexion angles (4.14°). Furthermore, the low-stiffness condition increased the magnitude of the rearfoot inversion (1.21°) and adduction (11.38°) angles and reduced the rearfoot abduction angle (12.1°). CONCLUSIONS: It is likely that reduced stiffness of the forefoot midsole stretched the plantar fascia, increasing rearfoot stability during the stance phase of gait. Increased muscular contraction may also explain increases in rearfoot stability. Therefore, the integrity of the plantar fascia and ankle muscles' force and resistance should be considered when choosing a shoe with reduced or increased forefoot midsole stiffness for walking.

Acute neuromuscular response during eccentric overload protocol by using a mechanical device to increase the load / Resposta neuromuscular aguda durante um protocolo de sobrecarga excêntrica usando um dispositivo mecânico para aumentar a carga

Abstract The aim of this study was to propose a mechanical device that could increase the mechanical load during the entire eccentric (ECC) action on a knee flexor machine and to compare the muscular activity when the device was used during a testing protocol. Fifteen physically active women were recruited, and they performed two protocols: control and eccentric overload. Control protocol was performed with concentric (CON) and ECC actions with similar load (60% of one repetition maximum) whilst eccentric overload protocol consisted of ECC actions with 40% more load than CON actions. Muscular activation was measured using surface electromyography of the biceps femoris (BF) and the gastrocnemius medialis (GM) muscles. ECC actions presented a higher muscular activation during eccentric overload protocol than control protocol for BF (p = 0.032), but not for the GM (p = 0.439). The mechanical device increased the mechanical load during the ECC muscle action and consequently increased the amplitude of the neural drive to the BF muscle; however, it did not increase the amplitude of the neural drive to the GM muscle.

Resumo O objetivo deste estudo foi propor um dispositivo mecânico que acoplado a uma cadeira flexora aumente a carga mecânica durante toda a ação excêntrica (ECC) e comparar a atividade muscular durante a utilização do dispositivo proposto. Quinze mulheres fisicamente ativas foram recrutadas e realizaram dois diferentes protocolos (controle e sobrecarga ECC). O protocolo controle foi realizado com ações concêntricas (CON) e ECC com carga iguais (60% de uma repetição máxima), enquanto o protocolo de sobrecarga ECC consistiu em ações ECC com 40% mais de carga do que as ações CON. A ativação muscular dos músculos biceps femoris (BF) e gastrocnemius medialis (GM) foi medida por meio de eletromiografia de superfície. Durante as ações ECC foi observada uma maior ativação do BF durante o protocolo de sobrecarga quando comparado ao protocolo controle (p = 0,032). No entanto, GM não apresentou diferenças na ativação entre os protocolos (p = 0,439). O dispositivo mecânico proposto foi capaz de aumentar a carga durante a ação ECC e, consequentemente, a atividade muscular do BF.

Late rearfoot eversion and lower-limb internal rotation caused by changes in the interaction between forefoot and support surface.

BACKGROUND: The influence of distal mechanical factors that change the interaction between the forefoot and the support surface on lower-limb kinematics is not well established. This study investigated the effects of the use of lateral wedges under the forefoot on the kinematics of the lower extremity during the stance phase of walking. METHODS: Sixteen healthy young adults participated in this repeated-measures study. They walked wearing flat sandals and laterally wedged sandals, which were medially inclined only in the forefoot. One wedged sandal had a forefoot lateral wedge of 5 degrees and the other wedged sandal had a forefoot lateral wedge of 10 degrees. Kinematic variables of the lower extremity, theoretically considered clinically relevant for injury development, were measured with a three-dimensional motion analysis system. The variables were evaluated for three subphases of stance: loading response, midstance, and late stance. RESULTS: The 5 degrees laterally wedged sandal increased rearfoot eversion during midstance and the 10 degrees laterally wedged sandal increased rearfoot eversion during mid- and late stances, in comparison to the use of flat sandals. The 10 degrees laterally wedged sandal produced greater internal rotation of the shank relative to the pelvis and of the hip joint, during the midstance, also compared to the use of flat sandals. CONCLUSIONS: Lateral wedges under the forefoot increase rearfoot eversion during mid-and late stances and may cause proximal kinematic changes throughout the lower-extremity kinetic chain. Distal mechanical factors should be clinically addressed when a patient presents late excessive rearfoot eversion during walking.