Brief Summary
Brusco, Clarissa M. 1,2; Pinto, Ronei S.1 ; Blazevich J.2
This study compares the effects of contraction intensity and mode on biceps femoris long-head fascicle behaviour, providing valuable insights into Bicep Femoris muscle function during different types of contractions. As the Bicep femoris is the most commonly injured hamstring muscle, these data may have important clinical implications.
How were the data captured and analysed to assess biceps femoris fascicle behaviour?
Biceps Femoris Fascicle Behaviour during Submaximal and Maximal Slow Speed Contractions were captured and analysed.
- Participants: The study involved 18 healthy adults (10 men and 8 women) without a history of right hamstring strain injury. Participants performed submaximal (55%) and maximal concentric and eccentric isokinetic knee flexions at a speed of 30°·s−1.
- Data Capture: BFlh fascicle length (Lf), fascicle angle (FA), and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices. Ultrasound videos were exported and edited to create a single, synchronised video for analysis. Three fascicles were analysed through the range of motion (10° to 80°).
- Analysis: Changes (Δ) in fascicle length (ΔLf), fascicle angle (ΔFA), muscle thickness (ΔMT), and muscle gear at short (60° to 80° knee angle) and long (10° to 30°) muscle lengths were measured and compared. The study compared the effects of contraction intensity (submaximal vs maximal) and mode (concentric vs eccentric) on fascicle behaviour.
- Findings: The study observed greater ΔLf at longer muscle lengths during both submaximal and maximal eccentric and concentric contractions. Additionally, no significant differences were found between submaximal and maximal contractions for ΔLf, ΔFA, or ΔMT. The architectural gear ratio remained relatively constant (~1.0 to 1.1) under most conditions.
By utilising ultrasound imaging and isokinetic contractions, the study provides insights into how contraction intensity and mode influence BFlh fascicle behavior at different muscle lengths and speeds.
How do submaximal and maximal contractions affect biceps femoris fascicle lengthening and rotation?
Submaximal and maximal contractions have been shown to affect biceps femoris long head (BFlh) fascicle lengthening and rotation differently. The study observed that a greater change in fascicle length (ΔLf) was observed at longer muscle lengths compared to shorter lengths during both submaximal and maximal eccentric and concentric contractions. Importantly, this mechanical effect was consistent regardless of contraction intensity.
Furthermore, the study found that both the change in fascicle length (ΔLf) and the change in fascicle angle (ΔFA) were similar in submaximal and maximal concentric and eccentric contractions performed from 10 to 80 degrees of knee flexion in prone.
What were the key findings regarding architectural gear ratio at long and short muscle lengths?
The study found that the architectural gear ratio, which represents the ratio of muscle-to-fascicle shortening, remained relatively constant at around 1.1 under most conditions, indicating a low and positive gear ratio. This consistency in the gear ratio was observed across different muscle lengths, contraction modes (concentric and eccentric), and intensities (submaximal and maximal).
The relatively low gear ratio observed in the study is consistent with previous research showing that low gears are utilised when muscle forces are high. The study suggests that the additional fascicle lengthening observed at longer muscle lengths was likely due to muscle stretch rather than substantial changes in fascicle rotation or muscle shape change. The similar gear ratio observed between contraction modes indicates that simultaneous alterations in both muscle and fascicle lengthening helped maintain the gear during both contraction types.
These data are consistent with both other research findings and clinical experience that have highlighted similar long terms changes in muscle (e.g. thickness, fascicle length) in response to high and low to moderate intensity isometric and isotonic strength training protocols. However, it is important to highlight that the general trend is certainly for training-induced changes in muscle to be most evident when training is performed at longer muscle lengths.
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https://pubmed.ncbi.nlm.nih.gov/37202880/