Lights weights with high reps, heavy weights with low reps, and building muscle are confusing to many. Conventional wisdom states that to get ripped, you need to lift heavier weights with moderate reps, while low weights at high reps were better for endurance.
The standard model of weightlifting for strength vs. endurance looks something like this, where repetition maximum (RM) is the max weight you can lift for one repetition:
So is there no hope for those who just don’t want to lift heavy weights to the point of max exertion but still want to gain muscle? Recent muscle science has something to say about that!
Reps vs Weight: The Science of Building Muscle
We first look to the 2012 exercise study with the lengthy title: Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Three groups of men who didn’t weightlift routinely were assigned different exercise regimens, all doing leg extensions, three times a week for ten weeks:
3 Sets of 30% RM for 30-40 reps
1 Set of 80% RM for 10-12 reps
3 Sets of 80% RM for 10-12 reps
You would expect that Group 3 would have had the most significant muscle gain. However, the results showed that Groups 1 (light weight, high reps) and 3 (high weight, low reps) were nearly identical in muscle growth!
To see if the same results bore out on men who already routinely train, the same research team then performed a similar study: Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men. This study used 49 men who had an average of 4 years of experience lifting weights. These groups performed whole-body workouts over 12 weeks, divided into 2 exercise regimens:
30-50% RM for 20-25 reps
75-90% RM for 8-12 reps
Here were the results:
“Skeletal muscle biopsies, strength testing, dual-energy X-ray absorptiometry scans, and acute changes in systemic hormone concentrations were examined pretraining and posttraining… Strength increased for all exercises in both groups (P < 0.01), with only the bench press difference between groups. Fat and bone-free (lean) body mass and type I and type II muscle fibre cross-sectional area increased following training (P < 0.01) with no significant differences between groups.“
So what can we take away from this? Lifting lighter weights with higher reps can help you build muscle - but there are some essential things to consider.
The science of muscle training and metabolic stress
Muscle damage, mechanical tension and metabolic stress are essential for muscle growth. For those who need a quick primer:
Muscle damage: sustained during resistance training due to eccentric contractions (lengthening of muscle) and concentric contractions (shortening of the muscle). That’s why it’s crucial to maintain control during all phases of a rep.
Mechanical tension: Created by a heavyweight load through a full range of motion.
Metabolic stress: The burn you feel at the end of a set when lactic acid builds up in the muscles.
Most people tend to veer towards heavy weights at low reps because they can achieve all three of these factors in a shorter amount of time. The bottom line is you can still increase muscle mass and lift light weights, but you need to do enough reps to achieve maximum volume: the amount of actual exertion on your body. If you’re not feeling the burn between sets, you won’t achieve optimal results.
Another reason you might not want to aim for 85-95% of your RM, mainly if you’re not very experienced with weight lighting, is it’s easy to mess up your form. Not only will this prevent you from gaining muscle, but it will also increase your chance of injury!
The bottom line of the light weight vs. heavy weight debate is - ensure you’re working hard!
How personal training can help you attain your goals
Ready to work on a better body? Frustrated that your solo workouts have not given you the results you want?
A personal trainer and custom strength training program can get you there. They will work with you to ensure you’re meeting the optimal RM and reps to suit your fitness level and goals while providing you with a custom meal plan to ensure you have the right fuel.
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