When it comes to strength training – and effective strength training with heavier weights, where the struggle to perform the last few reps – your muscles needs a day’s rest before being worked again. If you want to train one day after the other, you need to split your workouts into upper and lower, and alternate between the two. That said, it only takes 3 moderately intense strength sessions a week to see significant results, so don’t feel bad for taking a day off.