Muscle-specific hypertrophy training part 2
Last week our tutor Katie Farnden explained how muscle fibre types influence the loads to use when training certain muscles. Here she explains the implications on contraction type and exercise selection.
Now we have established suitable repetition ranges, intensities and rest periods we can also think about the speed of movement and contraction research.
Eccentric movements have been shown to recruit the most fast twitch fibres. Research from McHugh et al (2002) concluded that during concentric contraction more muscle fibres are active. However, the eccentric phase increased the mean frequency of the EMG signal. This suggests the recruitment of more fast twitch fibres, allowing for greater muscle growth. This is especially true with the hamstrings, which are fast twitch during knee flexion and slow twitch during the extension.
In conclusion, if you want to train your fast twitch fibres of the hamstrings, or to recruit more fast twitch potential from the glutes, then eccentric contraction should be emphasised with an explosive movement during the concentric phase to recruit as many muscle fibres as possible.
Is this the whole puzzle of specific muscle training? Whilst this is important it is not the only factor to consider. We must also take into account the biomechanics. Typically the hip joint can hyperextend 10° with bent legs and 20° with straight legs, so what implications does this have? Well, when studying the relationship between force and length, the glutes contract the most between these two ranges of degree, producing greater force when at their resting length compared to their contracted or lengthened state.
In addition they work alongside the hamstrings during hip extension, relying on the hamstrings to flex the knee. This dual function is important when considering which exercises to incorporate. If the hamstrings try to stretch at the hip and the knee, or flex at the hip and knee simultaneously, they enter active insufficiency due to shortening and inability to fully contract with force. This means that during exercises such as dead lifts, if the knees remain bent, or during glute bridges, emphasis is placed on stimulating the glutes, whereas a straight legged position will favour the recruitment of the hamstrings due to maximum muscular tension in that stretched state.
A good hamstring workout will incorporate straight legged exercises stretching the muscle fascia and a variation of leg curls to contract the heads of the muscle at various points. It is the inclusion of these leg curls that also induce high levels of metabolic stress and muscular damage by activating the lower hamstrings to a greater degree than the favoured deadlifts. The hamstrings, however, still have a small amount of slow twitch fibres present, so it would make sense to still adopt training methods that are effective for both fast and slow twitch whilst still prioritising those of fast twitch.
Overall we can summarise that an optimal training programme should be muscle specific, analysing the muscle, its biomechanics and fibre type to establish the correct volume and intensity best suited to its genetic make-up and goals. Only then can we maximise and fulfill our body’s capabilities and potential.
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