Can cycling with single leg improve endurance and increase slow twitch muscles with shorter workouts?

Question

Can cycling with single leg improve endurance and increase slow twitch muscles with shorter workouts?

Theory

When muscle groups fatigue, they start to recruit larger motor units. That may explain why when you're exhausted, the workouts feel harder, and why polio victims fatigue sooner.

With single leg cycling, one leg VO2 max is close to that of two legs. That means the larger motor units can be targeted sooner given the same oxygen consumption. More of our muscle fibres would be given the signal to increase capillary density, increase mitochondria, increase mitochondrial enzymes, increase antioxidant defenses, and other kinds of adaptations.

My understanding

Based on my understanding, if we cycle 1 hour with one leg, the exercised leg may think it exercised up to 2 hours in terms of recruitment pattern! Having a meal in between two rides may refuel the smaller motor units, preventing some of the larger motor units from being trained.

Possible benefits

If this works, we may be able to break fitness plateaus or maintain endurance with more flexibility in our schedules. According to some commentators, long rides should be done all in one go so biking to work, working 8 hours, and riding home feels different for our bodies than riding twice the distance to work then staying overnight at work.

If you're doing group rides, it can help the slower riders keep up with you while you have a good workout.

It may also decrease blood pressure because a study showed that higher type I fibres reduce blood pressure. https://www.ncbi.nlm.nih.gov/pubmed/15837823

Another benefit is that the exercised leg could push harder than in two-legged workouts at a lower heart rate without causing breathlessness. Those with health problems such as hypertrophic cardiomyopathy or high blood pressure may need to limit their heart rate during exercise to stay safe.

Challenges

What we may need to do is make sure that we don't pull on the upstroke. We might use the counterweight on the pedal of the unused side or redesign the chainrings to make the upstroke easier. We also need to remember to exercise the other leg on another workout.

Does this actually work in practice?

Answer 1

Working out one leg at a time in the stated way does not shorten your workout time.

If your assumption is correct it says: 1h per leg equals a workout of 2h normal training, but you have to do 2h to get both legs trained. In the end, you get a 2h workout in 2h.

If you want to push harder, it would be easier to just choose a harder gear.

Answer 2

There's an assumption in the question that one legged cycling can be almost as hard work as two-legged, and in the same way - "With single leg cycling, one leg VO2 max is close to that of two legs." I've done a little one-leg cycling myself and think that's harder than it sounds.

The sensors on the WattBikes at my gym showed my left leg was contributing less than my right when tired when I'd had a couple of months off with a broken shoulder and was still not cleared to ride outdoors though I was encouraged to exercise. So I tried using my weak leg alone for some intervals.

I'd say there are a couple of problems with this. I'll assume an indoor trainer. These points will also be true on a moving bike, where there would be other problems as well.

• Bikes aren't really set up for riding with one leg idle so you need to work round that.

  • You can keep the idle foot (clipped) on the pedal and carry it round, but you'll tend to use it a bit.
  • You can find somewhere to put it out of the way, which changes your position on the saddle and ability to deliver power or high cadence.
  • Even if you take a pedal off (extra time lost to fiddling around, and only possible if you own the kit) the crank still swings around.
  • It's probably easier on a recumbent trainer, but have you got access to one, and is it suitable for hard efforts? The ones I've seen in gyms aren't.

• Standing up on one pedal is very different to standing up on two, e.g. for high power, high force training. That's not to say it wouldn't be beneficial, but getting over top dead centre is awkward and pulling up at the back of the stroke both necessary and almost impossible without sitting down (completely impossible when I tried it as I couldn't pull up on the bars). A trainer with more inertia would help a lot, like riding a flat road instead of uphill.

• Even seated (good for high cadence work at least), you have to pull up on the pedal, and most of us aren't very good at that*. This study (well worth a look) added a counterweight to the other pedal - helpful if that's an option, i.e. on a trainer you own, rather harder on a gym bike or one that needs to be fit. The counterweight would need to be correct, and the paper credits it with a lot of the training benefit. While that paper doesn't say how it was selected, it references this poster, of which only the text is available, but that says 20lbs was optimal.

• Looking at the study linked in the comments under the than most of us would consider training other answer (COPD patients), this was at far lower intensity and duration (15 minutes per leg 3 times per week as their main aerobic exercise). We should be very wary of extrapolating from that to people who are starting well-trained.

The first two points (backed up by my own experience) suggest that it would take some time to get used to it and find a way of working. That's an investment in training time that might not lead to returns. If you stick with it through these steps, you might get some benefit, but even then Power meters that give independent readings for each foot will increase your options. Once you've overcome the initial hurdles and got a decent setup, there might be some benefit to interval training, according to the paper I linked.

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* Pedalling by pulling up at the back of the stroke instead of pushing down is interesting training in its own right, and a relief on long rides after a climb flattens out. That would be a better fit for a stronger rider in outdoor group rides than anything involving fiddling with kit (though carrying the idle foot round is also an option there).