The reason why human athletic levels are where they are have nothing to do with control and everything to do with tolerances. This is actually a similar reason to why being in a car accident or falling off a cliff is so dangerous; the human body is not designed to go at those speeds or 'jump' that high. For one thing, our bones are designed to be strong but still relatively light. They support us perfectly well in running, jumping, dancing, lifting some heavy things, but they can't take stresses that occur at driving speeds or from falling off high buildings or cliffs.
The same is true of your tendons; they are designed to hold your muscles to your skeleton and in normal use are more than up to the task. But, try to lift a car and assuming you get it up, there's a very strong chance that you'll tear a ligament. Athletes are constantly doing this and anterior cruciate ligament (ACL) tears are a common injury that they suffer even now.
Your Frenchmen won't be able to run super long endurance events like 10x marathon distances because this requires extra energy that has to be stored somewhere in the body and released in a constant manner to the active muscles and there's some evidence to say that even regular marathons can be damaging to a body over the long term because of the way the body stores and supplies energy.
Your Frenchmen also won't be able to run sprints in a tenth of the time Usain Bolt can do it because the muscles can only twitch so fast and accelerating that, even if possible, is only likely to tear the aforementioned ligaments; essentially the muscles would tear themselves off the bones.
Your Frenchmen also won't be able to lift cars or jump buildings or the like because the skeleton won't be strong enough to support the weight or take the impact of landing. Alright, that's not strictly true; it may be able to do it for a while but the price you're going to pay is that your body is going to give out a lot earlier than it otherwise would.
Even tradesmen and athletes today, without emulating super powers, suffer from a range of health problems in their later life. Many have worn cartilage, joint (especially knee) issues, arthritis and a stream of other wear to their bodies that limit their ability to perform basic tasks in their later years.
Put simply, your Frenchman still has a standard body that can only be pushed so far in its lifetime, regardless of how much control you may have over it.