Hamstrings and Leg Curls

April 22nd, 2007 by

Leg Curls …. Do them? Don’t do them? There’s a lot of villfying of leg curls going on by various people these days. Now, I’m not going to argue their logic, because well, in the context of their arguement, they’re right. One of the criticisms is that leg curls aren’t ‘functional’ (popular word these days), and the hamstrings don’t function in isolation of the glutes in the ‘real world’ – hence the alternatively recommended SHELC (supine hip extension w/ leg curl) exercise. With this execise both the glutes and hamstrings are working together. So, much of the criticism stems from an ‘athlete’ or functional versus non-functional standpoint. Beyond saying that more people would be better off paying more attention to the hip extension function (think deadlifts variations, pull throughs, single-leg RDLs, etc.) of the hamstrings instead of so much attention to the knee flexion function of the hamstrings (leg curl variations), I’m going to leave that issue alone. Do them or don’t do them; it’s up to you. But from a developmental standpoint (ie. more muscle), any exercise that places tension on a muscle and allows you to increase that tension (ie. add more weight) over time, can create a hypertrophic response. Progressive overload + sufficient nutrients = muscle growth. Anyway, what I wanted to quickly address was a question I often get in response to my suggestion to point the toes when doing leg curls. I invariabley get a follow up email where I’m told how much a person’s calves were cramping up. So here’s the deal … The calves are what are known as a biarticular muscle, meaning they cross two joints – both the knee joint and the ankle joint. This means they serve multiple functions. One, they obviously plantar flex the ankle. However, they also assist in knee flexion (ie. leg curls). Most people will do lying leg curls with their ankles dorsi flexed – toes pulled towards the shins (opposite of a calf raise). In this position, the calves, since they are not working to plantar flex the ankle, can assist in the flexing of the knee. So what happens here is that you can use more weight, since BOTH your hamstrings and calves are functioning to bend the knee. However, if you flex the calf, they can no longer assist in knee flexion, since they’re already busy working at the other joint. So, in this position, your hamstrings are forced to do all the work as the calf assistance is inhibited. End result? Harder working hamstrings. Now, since most people (meaning 99 out of 100) do them the first way – since (1) it seems more natural and (2) you can lift more weight (obviously since both hams and calves are working), when you try them the other way, your calves are going to cramp up. Why? Because the neural pathways for this exercise have been established and your body is used to recruiting the calves to help. BUT, youve ‘disabled’ them. So your body will try to get them to help – hence the cramping – but wont be able to. This decreases over time as you reestablish new recruitment pathways. You could ease into this by doing the concentric with your ankles dorsi flexed (hams + calves) and doing the eccentric with your ankles plantar flexed (hams). Then over time you could move to doing both the concentric and eccentric with your ankles plantar flexed.