1 day ago
The Muscles & Hypertrophy Series - Part Six
Only those muscle fibres that are both recruited and fatigued adapt.
Each Motor Unit contains a spectrum of muscle fibres types, from fast twitch (FT) to slow twitch (ST).
It isn’t actually the case that LTMU’s contain only ST fibres and HTMU’s only FT, it’s that HTMU’s contain both more total muscle fibres and a greater ratio of FT fibres.
Different muscles have different ratios of ST to FT fibres, which would suggest they’d respond better to slightly different rep ranges (though they’ll still respond to any).
For example, the Soleus muscle (deepest lying calf muscle) is on average 80% ST (with a range of 64-100%), while the Gastrocnemius muscle (top lying calf muscle) is about 50% FT, 50% ST (with a range of 34-82% FT).
Therefore Soleus may be better suited to slightly higher rep ranges due to its higher ratio of ST fibres.
Gastrocnemius meanwhile may be better suited to slightly lower rep ranges because of its higher proportion of FT fibres.
We might therefore decide to use a rep range of 5-10 on a Standing Calf Raise (Gastrocnemius dominant) while using a range of 15-20 for a Seated Calf Raise (Soleus dominant).
This doesn’t mean we shouldn’t use a variety of rep ranges.
It just means that a ST dominant muscle may be best hypertrophied through the use of higher rep sets taken very close to failure (in order to get those effective reps).
While a FT dominant muscle may be best hypertrophied through the use of lower rep sets (also taken within 5 reps of failure).
Finally, we must respect the governing principle of Progressive Overload.