In the older version, it didn't have that logic. It was more random.
I bought a fast trainer and power-trained him with 3 bars/practice in a row so to gave him 50 sp (for sa), without any injury
but sometimes when I didn't want to waste some condition of one player (when it was time to replenish condition and he had a full bar), I gave him 2 bars in stretching or cardio and had an injury - lol