Lifting light weights is typically only useful for one thing: burning calories. Say you lifted a light weight 20 times and you could lift a weight twice the mass of the light one 10 times, you would not build muscle by lifting the lighter one. To better explain it, use logic to show why it makes sense. If you lift a pencil 1,000,000 times a day you might be doing the same amount of work as lifting a 10 kg weight 10 times a day. However, doing the same amount of work does not equate to the same results.You aren't putting any pressure on your muscles by lifting a pencil 1,000,000 times a day, while lifting a 10 kg weight 10 times a day would require more muscular focus as you're lifting. Lifting heavy weights helps you build lean muscle, but you have to lift them for a considerable amount of repetitions. What do you think would build more lean muscle? lifting 20 kgs once or 5 kgs 4 times? It's the latter, since your muscle has to be focused for longer.So how about when you have a muscle building program and it tells you to follow a strict lifting schedule, like 3 sets of 15 reps. Should you opt for lifting a heavy weight and failing to finish the sets or using a lighter weight, finishing the sets but not really putting your muscles under any major strain? In this case, it's better to lift with heavier weights to push your muscles to failure. You shouldn't be bound by how many sets or reps you do. You should listen to your body for which weight it reacts to better. Having said that, don't lift an outrageously heavy weight. If you want to build muscle, lift a heavy weight many times.
