Weightlifting lore – more inclusive than it sounds – dictates that if you’re looking to build size, the smart money is on forcing your muscles to adapt by testing them with increasingly heavier weights. Each repetition of a movement, or ‘rep’ should be at the same weight, with a certain number of reps bunched together in a given number of ‘sets’. All very gym-speak but sensical nonetheless.
But the practicalities of pumping up your muscles extend past vanity. Not only do they help protect your bones, thereby reducing your chances of injury as you get older, but bigger muscles may also help keep your brain sharp, while one study found that heavier weights can even help with your cardio.
But when it comes to knowing how many reps is too many for you, the internet isn't always your friend. Arnold Schwarzenegger told Men’s Health that he likes to finish a workout with a casual 360 rep bodyweight workout. Which is not sound advice for the masses. More is better, but in moderation with a 2022 meta review suggesting that you can get stronger by 15 reps of light weight per set.
We all have different goals, so it makes sense to give your rep ranges some proper thought, instead of blindly following training plans that might not be optimised for you. To that end, we consulted the best PTs around to get their expert – and varied – advice in figuring out how many reps is right for you.
Understand what muscles are first
We think about muscles in the gym all the time, but how often do we actually think about them as functional pieces of tissue connected to all sorts of ligaments and tendons, each one with a different purpose?
“Skeletal muscles have two types of muscle fibres, slow-twitch and fast-twitch,” explains Leon Veal, head of R&D at STYRKR.
Slow-twitch fibres are geared more towards endurance and thrive in sustained, low-intensity activity. Fast-twitch fibres are used for explosive, high-intensity movements but fatigue quickly.
If strength and power is your aim, Veal recommends one to five repetitions per set at a higher intensity (around 85-100 per cent of one-rep max). If you’re trying to build size, up it to 8-12 repetitions per set at a moderate intensity (around 65-85 per cent of one-rep max). To stimulate those slow-twitch fibres and build resistance, aim for 13-20 repetitions per set at a lower intensity (around 50-65 per cent of one-rep max).
Vary reps depending on the workout
Not all workouts are created equal, so why are you still doing four sets of ten for every single exercise?
“In the case of workouts designed to enhance muscular endurance, like pushups or squats, I would recommend 15 reps max,” says Tomi Akande, PT at UNTIL.
Sure, you might be able to do more than 15 push-ups, but Akande says that going too far combined with inadequate recovery can lead to microtraumas in the muscles, and even hormonal imbalances that can mess up your cortisol levels, impacting muscle growth and overall health.
As a rule of thumb: focus on form and quality over quantity.
Start low to build functional strength
Following on from the last point, specialist equipment, like the TRX rig, may require an even more considered approach to reps, as Joanna Dase, fitness coach at Curves, explains.
“If you’re new to TRX, it’s important to start with 8-12 reps per set to build foundational strength. Focus on practicing your form and achieving a full range of motion, even if it means you can’t perform as many reps.”
If you’re bored with that, upping to 12-15 reps will help tone your muscles, as well as enhancing your stability. For the advanced TRX practitioner, Dase recommends 15-20 reps per set, incorporating more challenging variations of the exercises while maintaining form.
Of course, the TRX rig may not be for you, but you can apply these same principles – or near enough – to some of the more fun bits of kit in your gym like the battle ropes, sandbags, bosu balls and plyometric boxes. The crucial thing is to experiment and not to run before you can walk, especially on new equipment.
Lower reps for a PB
If you’re working towards upping your one rep max, it makes sense to do fewer, heavier reps. For Kieran Sheridan, co-founder and physiotherapist at Gulf Physio, “Three to six reps per set is ideal. If you’re lifting close to maximum weight with each set, it will result in improved strength development.”
“For maximum strength we look at 1-6 reps,” adds Ollie Weguelin, director of Sustain Performance. “For heavy weights, you’ll be working at a higher intensity and lower rep range. This is ideal for deadlifts, squats, bench presses and Olympic lifting.”
On the other hand, Sheridan says that beginners just looking to tone up might aim for a maximum of 20 reps per set. “If you can implement above 20 reps, there is a chance that you are practicing with light or easy weights, which will not help you improve or grow,” he warns.
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Stop if form and sleep break down
“Signs that working volume is getting too high would be a breakdown in form, struggles with sleep and even appetite fluctuations,” warns Alasdair Nicoll, a personal trainer at The Fitness Group.
Any of the above indicates that the central nervous system is struggling to recover at the rate it normally would. “The central nervous system prioritises rest and recovery from both a physical and neurological perspective, so the signals being sent to the muscles will not be as efficient as normal which will,” warns Nicoll. By keeping it working, you not only aren’t letting your body rest, you’re putting yourself at risk.
“A breakdown in form could look like the back beginning to curve in a deadlift where you would normally manage to maintain a neutral spine, or potentially the rounding of shoulders in a chest press,” warns Nicoll.
Cater to injuries
If you’re a gym regular, chances are you’ll be battling one injury or another constantly. You don’t need to stop training here, but you should think about rep ranges as a way of aiding recovery, and maintaining strength while you heal. An oblique injury impacting your ability to press overhead? You might consider dropping the weight and focusing on single-arm presses until you’re healed up.
“It’s very important to get the rep range correct when you’re injured,” says Chris Antoni, founder of Tailor Made Fitness.
But, Antoni warns “It’s not about picking a random number and hoping for the best as this will more likely cause more damage or not enough stimuli to help improve the injury.”
For example, if you’ve been given the all-clear following an ACL injury, Antoni recommends hitting 15-20 reps of light weight to start boosting the muscular endurance of the muscle in and around the affected knee.
“Once the knee gets stronger, lower the reps to the 10-12 rep range and increase the weight so the muscle starts working in the hypertrophy phase,” Antoni advises. “This will help restore knee stability, muscle strength and function.”
Think outside the box
Ultimately, exercise is not an exact science. There is no magic rep number for hypertrophy, and rep limits are dependent on all the usual factors from your age to fitness experience to whether or not you’ve had your coffee before hitting the gym.
“The ideal number of repetitions per set for muscle growth isn’t limited to the 6 12 rep range,” warns Adam Enaz, PT and registered dietician. “In fact, research indicates that there isn’t a significant difference in muscle growth based on rep ranges.”
Mixing repetition of ranges might actually be the way to go, at least according to a recent study that found that combining high and low loads leads to increased muscle growth and fat loss.
