In young male rugby players who lift weights, doing high-rep, lighter weight workouts leads to worse sprinting and agility performance for up to two days compared to low-rep, heavy weight workouts.

For young male rugby players who lift weights, doing high-rep, lighter weight workouts seems to slow them down and make them less agile for a day or two more than doing low-rep, heavy weight workouts.

Young male rugby players who do high-volume muscle-building workouts might see a small drop in their jump performance compared to those doing heavy strength training — but the results aren't super clear because different equipment was used.

For young male rugby players who lift weights, doing more reps to build muscle might slightly hurt their jumping ability compared to training for pure strength — but the measurement wasn't perfect, so we're not totally sure.

Lifting more weights each week makes you stronger, but the extra strength you gain from each additional set gets smaller faster than the muscle gains do.

If you're a young guy lifting weights more often each week, you'll build more muscle and get stronger—but after a while, your strength stops improving fast, while your muscles keep growing a bit longer.