One Leg Good - Two Legs Bad?
I currently have the joy of three of my children in secondary school. A lot of what they’re learning these days is well beyond anything I can remember from my own school days, but one familiar book keeps coming up: George Orwell’s Animal Farm.
I distinctly remember the slogan, “Four legs good, two legs bad,” which later becomes “Four legs good, two legs better.” It reminds me of a debate I see regularly on social media about strength training for runners. We run on one leg at a time, so surely we should do our strength training on one leg too. Before long, it starts to sound like “one leg good, two legs bad”.
I can understand the question. Watch a runner and you’ll see one leg supporting the body while the other moves through the air. A squat looks quite different. But when I put an exercise in someone’s program, I’m looking at what it will help us develop. How much it looks like running is only part of that decision.
When I prescribe a squat for a runner, I’m looking at how much force they can produce relative to the bodyweight they need to move. In a sprinter who struggles to build speed out of the blocks, for example, I’d want to know how much of the problem comes from force capacity and how much from applying it effectively. A squat lets us progressively load the hip and knee extensors from a stable position, adjusting the depth, resistance and intent of the lift according to what we need to develop. Having both feet on the ground helps us keep the emphasis on force production, with less demand on balance than an unsupported single-leg exercise.
There is a trap here, though. The bigger weight on the bar doesn’t automatically mean each leg is working harder than it would in a split squat. Both legs share the load in a squat, and in either exercise the athlete is moving some of their bodyweight as well. Comparing a barbell with the dumbbells someone holds for a single-leg exercise doesn’t tell us which is challenging the working leg more.
A split squat or step-up can be a substantial strength exercise in its own right. We can load each side separately and, depending on the exercise, ask the athlete to control the pelvis and trunk while producing force through that leg. Some of what we call single-leg training also uses support from the other foot. In a split squat, for example, the rear foot helps support the movement while we emphasise the front leg. That support can be useful when we want to load the leg heavily.
Compare that with someone wobbling through a single-leg Romanian deadlift. They put the other foot down, reset, try again and eventually stop because they keep losing balance. Their hamstrings and glutes might have had plenty more work available. If I want to develop their strength, I might have them put a hand on a rack so they can control the movement and load the working leg properly. There may be a reason to challenge their balance as well, but I want to be clear about which job we’re asking that exercise to do.
Neither a squat nor a slow single-leg exercise fully prepares someone for what happens when they run. During a heavy lift, there’s much more time to produce force than there is during a running contact. Standing on one leg doesn’t change that. The runner still needs to direct force appropriately and coordinate the legs, trunk and arms at speed while repeatedly landing and pushing off.
So the running itself remains essential, along with appropriate jumping, hopping or other reactive work. Getting stronger gives us something useful to work with, but we still have to train the athlete to apply force quickly and coordinate it with the rest of the running action.
The research hasn’t produced a simple winner between single-leg and two-legged training for sprint performance either. Strength gains tend to favour the type of exercise being trained. That helps explain why I’d choose exercises around what an athlete needs to improve, rather than assume one approach will always be better.
In a gym session, that might mean three sets of five in a squat variation followed by two sets of six split squats on each side. The squat might provide our main exposure to heavy loading, with the split squat adding work for each side and a different demand on pelvic control. For another athlete, I might use a supported split squat as the main strength exercise and adjust the rest of the session around it. That choice would depend on where I can get the training effect we need at a workload they can recover from.
For a Masters runner, I also need to know which exercises they tolerate, what equipment they have and how the gym fits around their running. An old injury might influence the choice. So might a demanding track session later in the week. And adding single-leg work means allowing for the time and effort of doing both sides; it can add up quite quickly if we simply put it on top of everything else.
I’m quite happy to have a squat and a split squat in the same runner’s gym program. I need to be able to explain why I’ve chosen each one, how we’ll progress it and how the amount of work fits around their running. The mix can change as their needs change through the season. I want the strength work to help them run better, and I’ll adjust the program according to whether that’s happening.
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