Hi friend, Your question: “Is lifting 100 lbs. for 15 reps better than lifting 150 lbs. for 10 reps?”, is like asking, "Is it better to eat a chicken burger or an apple?" It all depends on your goals. If you're trying to lose weight, the apple is the better option. But if you're trying to bulk up, the chicken burger is the way to go. In the same way, lifting 100 lbs. for 15 reps is better if you're training for endurance. But if you're trying to build muscle, lifting 150 lbs. for 10 reps is the better choice. Here's another analogy: Imagine you're trying to climb a mountain. You could take the long, winding path, or you could take the steep, direct path. The long path is easier, but it takes longer. The steep path is harder, but it's faster. Lifting 100 lbs. for 15 reps is like taking the long, winding path. Lifting 150 lbs. for 10 reps is like taking the steep, direct path. Here's some depth: Lifting heavier weights for fewer reps stimulates m...