Neuromuscular factors influencing the maximum stretch limit of the human plantar flexors

Maximum joint range of motion is an important parameter influencing functional performance and musculoskeletal injury risk. Nonetheless, complete description of the muscle architectural and tendon changes that occur during stretch and the factors influencing maximum range of motion is lacking. We measured muscle-tendon elongation and fascicle lengthening and rotation sonographically during maximal plantar flexor stretches in 21 healthy men. Electromyogram (EMG) recordings were obtained synchronously with ultrasound and joint moment data, and H-reflex measurements were made with the ankle at neutral (0°) and dorsiflexed (50% maximal passive joint moment) positions; the maximum H amplitude (normalized to maximum M-wave amplitude; Mmax) and H-amplitude elicited at a stimulation intensity that evoked 10% Mmax were obtained. Maximal stretch was accomplished through significant muscle (14.9%; 30mm) and tendon lengthening (8.4%; 22mm). There were similar relative changes in fascicle length and angle, but planimetric modelling indicated that the contribution of fascicle rotation to muscle lengthening was small (<4mm). Subjects with a greater range of motion showed less resistance to stretch and a greater passive joint moment at stretch termination than less flexible subjects, i.e. greater stretch tolerance. Also, greater fascicle rotation accompanied muscle elongation (9.7 vs. 5.9%) and there was a greater tendon length at stretch termination in more flexible subjects. Finally, a moderate correlation between the angle of EMG onset and maximum ROM was obtained (r=0.60, p<0.05), despite there being no difference in H-reflex magnitudes between the groups. Thus, clear differences in the neuromuscular responses to stretch were observed between 'flexible' and 'inflexible' subject

Influência do intervalo de tempo entre as sessões de alongamento no ganho de flexibilidade dos isquiotibiais Influence of the time interval between stretching sessions on increased hamstring flexibility

CONTEXTO: A otimização do treino de flexibilidade está relacionada com o uso de parâmetros adequados de alongamento. Entretanto, o intervalo de tempo adequado entre as sessões de alongamento tem sido pouco investigado. OBJETIVO: Verificar se a variação no intervalo de tempo entre sessões de alongamento influencia no ganho de flexibilidade. MÉTODOS: 28 mulheres, com idade de 22,5 ± 1,8 anos, foram distribuídas aleatoriamente em três grupos. Aplicaram-se 10 sessões de alongamento nos isquiotibiais do membro direito. O grupo 0X (n = 8) foi o controle e não recebeu alongamento. O grupo 3X (n = 10) alongou três vezes por semana (intervalo de 48 horas) e o grupo 5X (n = 10), cinco vezes (intervalo de 24 horas). Aplicaram-se 10 sessões de alongamento (sustentar-relaxar) nos isquiotibiais direitos. As medidas foram tomadas por análise fotométrica no programa AutoCad® 2000. A análise estatística foi realizada com ANOVA e teste post hoc de Newman-Keuls adotando um p-valor referencial de 0,05. RESULTADOS: Após 10 sessões, identificou-se aumento da flexibilidade nos grupos experimentais, porém sem diferença entre estes. O grupo 3X aumentou significativamente a partir do 10º dia do programa (quinta sessão) e o grupo 5X, a partir do terceiro (terceira sessão). CONCLUSÕES: O alongamento aumenta a flexibilidade dos isquiotibiais, independente do tempo entre as sessões (24 ou 48 horas); e a variável tempo não influencia o ganho de flexibilidade total. Porém, com cinco sessões semanais, ganha-se flexibilidade mais rapidamente. Isso sugere que o ganho de flexibilidade é sessão-dependente.<br>CONTEXT: The optimization of flexibility training is related to the use of ideal stretching parameters. However, the time interval between sessions has been little investigated. OBJECTIVE: To verify if the variation in time interval between stretching sessions influences in flexibility gain. METHODOLOGY: Twenty-eight women, average age of 22.5 ± 1.8 years, were randomly distributed into three groups. Group 0X was the control and performed no stretching. Group 3X (n = 10) took part in three sessions per week (interval = 48 hours) and group 5X (n = 10) in five times (interval = 24 hours). Ten stretching sessions were applied (hold-relax) to the right hamstring. The measurement of active knee extension was performed using photometric analyses on AutoCAD® 2000 software. Statistical analysis was carried out with ANOVA and Newman-Keuls post hoc test for a significance level of p < 0.05. RESULTS: After 10 sessions, increased flexibility was identified in the experimental groups (p < 0.01), but with no difference between them. Group 3X significantly increased flexibility from the tenth day of the program (fifth session) and group 5X from the third day (third session). CONCLUSIONS: Stretching increases hamstring flexibility, regardless of the time between sessions (24 or 48 hours). Moreover, the interval between the sessions does not influence total flexibility gain. However, with five weekly stretching sessions, flexibility increases more rapidly than it does with three, suggesting that flexibility gain is session-dependent