Effects of hip extension and knee flexion submaximal exercises until exhaustion on hamstrings stiffness

• Autor(a) principal: Almeida, Pedro Nuno Martins de Carvalho
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.5/28579
• topic: Shear modulus; Skeletal muscle; Hamstrings; Fatigue; Elastography; Shear modulus; Músculo-esquelético; Hamstrings; Fadiga; Elastografia; Domínio/Área Científica::Ciências Sociais::Outras Ciências Sociais

Purpose: The research interest in hamstrings muscle group has substantially increased in the past years mostly due to the growing injury rate, more prevalent in biceps femoris long head (BFlh). Recently, an altered recruitment pattern between BFlh and semitendinosus (ST) with fatigue has been suggested as a factor underlying the injury occurrence. However, it is unknown whether the recruitment alteration of these biarticular muscles reflects changes in their stiffness during contraction (i.e. active stiffness) with fatigue, in particular during hip extensor (HE) vs. knee flexor (KF) tasks. This study investigated the effects of a HE vs. KF submaximal isometric contraction until exhaustion on the hamstrings: semimembranosus (SM), ST and BFlh, adding bicep femoris short head (BFsh) for KF and gluteus maximus (GM) for HE. Methods: Fifteen individuals (age: 23.3±3.5 yrs.; height: 1.74±0.05m; mass: 70.7±9.5kg) participated in two sessions separated by 7 days, where a hip extension (i.e. lying prone, hip flexed at 10º, and knee full extended) and knee flexion (i.e. lying prone, hip neutral, and knee flexed at 20º) fatigue task with a randomized order was conducted. The fatigue protocol consisted in performing an isometric contraction at 20% of maximum voluntary isometric contraction until exhaustion. Before and immediately after the tasks, selected muscles (HE- ST, SM, BFlh, GM; KF- ST, SM, BFlh, BFsh) active stiffness was measured (2 trials each), at the muscles mid-belly, during 30s contractions at 20% and 40% of MVIC, in a randomized order. Active muscle stiffness was assessed with ultrasound-based shear wave elastography (i.e. through shear modulus quantification), using two similar ultrasound scanners (v11, Aixplorer), one for each muscle. Two-way repeated measures ANOVAs [moment (pre/pos) ✕ joint (hip/knee)] were conducted to examine the fatigue effects, and paired samples t-tests or Wilcoxon tests (depending on normality) were used to measure interactions between moment*intensity. Significance level was set at 0.05. Results: For HE task, we observed for SM a main effect for moment factor (p=0.008). After post-hoc, results showed a decrease in stiffness after fatigue (Pre: 54.2±2.5 kPa; Post: 44.6±3.6 kPa), only present for this muscle. In KF task, for ST active stiffness, we observed a main effect for moment (p<0.001), intensity (p=0.001) and interaction effect (p=0.007). Post-hoc revealed that ST active stiffness was greater pre than post-fatigue (Pre: 76.9±5.9 kPa; Post: 63.5±3.8 kPa) and higher with more intense contractions (20%: 58.0±3.1 kPa; 40%: 82.4±7.1 kPa). For interaction effects, it was revealed a difference between pre- and post-fatigue at 20% MVIC (p<0.001). For BFlh it has shown main effects for both moment (p=0.021), intensity (p=0.002) and interaction (p=0.002). Post-hoc analysis revealed active stiffness with lower values after fatiguing task (Pre: 49.9±2.8 kPa; Post: 54.2±3.1 kPa) and for higher intensities (20%: 45.0±3.2 kPa; 40%: 59.0±3.6 kPa). For interaction were observed significant differences at 20% MVIC only (p=0.001). In both tasks, all muscles were also found a main effect for intensity, except for SM in KF (p=0.144). Conclusions: The present study findings suggests that knee flexor fatigue task, but not hip extensor, can alter the BFlh-ST active stiffness pattern (especially for 20% MVIC) favoring a greater BFlh overload. These findings are promise and open new perspective toward the understanding of hamstring injury. Regarding hip extension, only SM showed a decrease, when can be related to lesser work capacity of medial compartment, eventually overloading BFlh. Additionally, it states active stiffness seems to be greater for higher intensity contractions.