High school strength and conditioning class was quite the spectacle. I wasn't in the class (I thought I knew more than the teachers), but a lot of my friends were.
Fortunately, they were young and nearly invincible. The problem is simply that they were going too heavy and weren't paying attention to their form.
Form is by far the most important thing to pay attention to when lifting heavy. It doesn't have to look like a machine or be perfect, but if you can't do the exercise correctly you're more likely to injure yourself.
So the question becomes - how heavy should you be lifting? Should you be stacking the weight on to get stronger and build muscle, or can you take it a bit lighter?
There's actually some really cool research on this. They didn't do it strictly with weight, but perceived effort and rep ranges.
Turns out the #1 thing that matters is your effort. How hard you push yourself, not how much weight you're using.
If it's 135 or 225lbs, it doesn't really matter - it matters how far you push yourself. If you leave reps in the tank with 225, but demolish yourself with 135 - you're probably better off with 135lbs.
But that's not the whole story. Eventually you get strong enough that those reps get ridiculous. 25 reps, 50 reps, 100 reps.. While you CAN do that, it's probably not a good idea.
Instead, give yourself a rep range. When you max out that rep range: increase the weight. If you can't hit the minimum rep range: drop the weight.
It's that simple. But if you have an exercise that scares you, or you can't feel like you can safely go heavy - just increase the reps. Grind the exercise out.
But don't forget to focus on recovery or else your effort will be wasted.
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