Going to the gym is intimidating enough, but not knowing how to pick the right weight to use for an exercise can make a novice’s trip to the gym even more uncomfortable. If you grab too light of a weight, you’ll feel you wasted your time, while too heavy of a weight can lead to injury.
But it is very important to grab the right weight. In a 12-week long study published in the Journal of Applied Physiology, researchers found that subjects gained the most strength when using a weight that corresponded to 70% of their 1 repetition maximum (meaning 70 % of the heaviest weight they could lift in the exercise).
J Appl Physiol. 2008. Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity. Holm L, Reitelseder S, Pedersen TG, Doessing S, Petersen SG, Flyvbjerg A, Andersen JL, Aagaard P, Kjaer M.
But it’s not safe or efficient to test your maximum strength in every exercise, and then pick 70% of that.
Instead, here’s what you need to do. In most cases, 70% of the heaviest weight you could lift corresponds to 10-12 repetitions. So you want to use a weight that allows you to do no fewer than 10 reps, and no more than 12 reps per set.
For example, if you can do seated rows with 50 pounds for 20 reps, you should try using 70 pounds for 10 reps instead.
Unfortunately, the only way to identify your 10-12 repetition range weight is by trial and error.
Start conservative and pick a very easy weight. Do six repetitions. If that is really easy, increase the weight by 10% and try again. Do this until you find a weight that is a challenge for 10-12 reps. It should take you about 3 minutes to find the right weight for each exercise in your program.