This method gives you a two fold benefit,
* When you so choose, you operate at the peak human condition. Not superhuman (as that would shatter your bones, ligaments, muscles ...) but peak human. This is very important for adventurers, soldiers, crime fighters, fire fighters, messengers ..., basically anybody who needs to be able to physically perform at high level intermittently.
* (The more advantageous one) You can maintain this peak condition for the long periods of time regardless your actual physical state.
If you can channel this virtual muscle mass, you are also able to avoid the drawbacks of exhaustion, by gradually exhausting the virtual muscles at no expense to your physical body. I.e. your sugar levels, lactic acid level, and other markers of exhaustion do not change the way they would had you used your actual muscles.
Two model situation: Imagine a fire fighter who is charged with, for example of 48 hours worth of peak human condition virtual muscles. It helps him in daily operations (when he needs to pry open a car door, carry out the victims, run in and out of burning buildings (Even in full sprint his oxygen depletion stays at rest state, as the virtual muscles are those burning the extra oxygen) or perhaps even handling a hose with water pressure, he would otherwise be unable to handle. 75
This boon is especially noticeable in case of prolonged activity. Imagine a natural disaster, such as flooding, with people trapped under the rubble, inside buildings and various currents, now imagine a unit of emergency responders who can operate at full speed, full strain for 24 or even more hours (essentially until brain needs a rest). Every mundane physical activity that needs to be performed can be performed by these people for tens of hours. Have you ever shoveled rubble? You get tired in under an hour. These guys, 13 hours later, they are still going fresh.
This would be a godsend for everyone who relies in his physical condition.
To put it into perspective per this article: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00947.2009 a human body can theoretically endure a run speed of 69 kmph (<PERSON> in his world record 100m sprint maxed out around 45 kmph). Imagine you can maintain this speed for 21 hours. In under a day, a charged messenger could run from Paris to Rome a distance of 1436 km (per google maps) less then 7 hours longer then via a car.
EDIT: Wrote the first version on mobile, so I expanded a little and cleaned it up. 209