As long as there is sufficient recovery, it is possible. Recovery dictates timing and frequency. Monitoring for signs of insufficient recovery is the most important aspect of high frequency training. You can modify by reducing frequency or modulating intensity. Or you can extend recovery either between bouts or between several bouts. This is where the science of exercise comes into the equation. If you understand the science, you will be able to adjust accordingly for every client.
There’s a new heart rate monitor out that measures heart rate variability during an exerciser’s recovery from high intensity exercise (lowering heart rate variability is correlated with recovery). I haven’t had the opportunity to play with one, but one of my clients has one and uses it to tell when his body is ready for another cycle trip into the hills. Something might help your individual clients learn their recov
ery rates after different types and intensities of exercise.