Does the weight you lift matter or how much you lift during your training session in regard to muscle growth. You can find a lot of information out there that says you must lift heavy to get big, however there isn’t much to back it up.
First, if we look at a comparison of frequency with matched volume we can see that volume is the key driver to muscle growth. Volume being (weight lifted multiplied by the number of reps and sets). Gomez et al. 2018 compared low-frequency and high-frequency splits with equated volume. One consisted of training each muscle group specifically ones a week; the next trained a full body routine training each muscle group multiple times a week. After 8 weeks they compared pre training and post muscle mass finding no difference between routines as far as strength and muscle gain. From this study we can see that muscle growth isn’t affected by how many times we train.
Next if we look at Schoenfeld et al 2018 where he compared low volume training routines to high volume in an 8 week training routine. At the end of the 8 weeks they compared strength and muscle gain between the 3 groups. The results showed no difference for strength gains between the low, moderate and high volume groups. On the other hand, the higher volume group they had a significantly greater increase in muscle size. This is further supported by (Klemp A et al. 2017) which found that when volume is equated rep ranges do not show significant difference in hypertrophy. Showing us, that muscle hypertrophy seems to follow a dose relationship between training volume and hypertrophy.
Now if we look at how intensity plays a role in hypertrophy we can see that it doesn’t really matter the weight being lifted at the moment but the total volume. (Schoenfeld et al 2015) looked at the effect of high intensity load training compared to low intensity and found that there was no significant difference between the two as far as muscle growth. But when it came to strength the higher intensity did better. ( Klemp et al 2016) compared different rep ranges with equated volume and their effect on muscle gain and also found no difference in muscle growth when the volume was equated, again supporting the idea that volume is one of the key drivers of hypertrophy. Lastly (Schoenfeld et al 2017) found that hypertrophy can be achieved with a spectrum of intensities even sub maximal.
So why does it matter that you understand what the intensities mean? Well, let’s say you do your squats with 200 lb for 10 reps, but your real 10 rep max is 250 (the amount of weight you can only do 10 reps with). You are taking away volume that you could be adding to your routine and contributing to more hypertrophy. So instead of doing 2500lb volume for one set you cut it down by 500. Now you can fix this by doing number of max reps that represent 200 lb to make sure you’re adding enough volume. If you don’t do this, picture you cut your volume by 20% each set of exercise for your whole routine you’ll be doing a considerably less amount of volume if you actually stuck to the right intensity.