How Lifting Heavy or Light Weights Affects the Body in Different Ways -

Resistance training is crucial for building muscle mass, but you'll get very different results if you lift light or heavy weights.
Popular workouts such as barre involve lifting light weights for many reps, but many other fitness professionals swear by lifting heavy weights for a small number of reps.
We spoke to personal trainers and scientists to find out how the two styles of training produce different results, and which is better depending on your goals.

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When it comes to fitness, there's a lot of conflicting, confusing advice out there.

While most experts seem to agree that incorporating resistance training into your workout regime is incredibly important, not just for aesthetic results but also for your overall health and longevity, quite what form this training should take is highly disputed.

One main issue is whether you should lift heavy weights with a low amount of reps, or light weights with more reps.

Low weight training might mean doing three sets of 40 bicep curls with a 2kg dumbell, whereas high-weight training might be three sets of five bicep curls with 14kg dumbells.

Of course, the latter method takes less time than the former, but that isn't the only difference.

According to human movement and elite performance specialist Luke Worthington, a Certified Strength and Conditioning Specialist, Integrative Corrective Exercise Specialist, and Master of Science in Biomechanics, training with "different sets, reps, and weights will produce very different results."

We spoke to various experts to find out more about the two types of weight-training, how the results differ, and hwo to know which method is best for you.

Lifting light may help you build a lean physique

Two popular workout classes of the moment are spinning and barre, both of which often incorporate work with light weights.

"Low weight and high repetition training is fantastic for those looking for defined and lean muscles without bulk," Barrecore founder and celebrity trainer Niki Rein, whose previous clients include Claudia Schiffer and Pippa Middleton, told INSIDER.

"Generally speaking, heavy weight training is geared toward adding muscle mass, whereas high repetition training creates longer-looking muscle as less power is needed and the entire length of the muscle is used to create each contraction," said Rein, who is a REPS Level 3 Advanced Fitness Instructor, REPS Level 3 Personal Trainer, and NASM Certified Personal Trainer.

A post shared by Barrecore (@barre_core)Feb 13, 2019 at 4:30am PST

"With high repetition training such as Barrecore, it creates a lactic acid burn on the muscle groups of focus creating a hormone reaction that occurs over the few days post-workout," explained Rein.

Ultimately, Rein says that by working out to the point that your muscles are beginning to burn and shake, which is commonly what happens with high repetition and low weight training, "you will effectively be melting fat for a few days post your workout and have an increase of energy."

Sticking to low weights but working at a high rep rate so your muscles end up shaking could lead to burning more calories afterwards, but that's not the only positive.

Light weights cause fewer injuries than heavy ones

"Working with light weights allows you to perform movements through your full range of motion properly and precisely," Ashley Verma, founder of boutique barre studio Define.London, told INSIDER. "Plus, the risk of injury is much lower."

It's also deceptively difficult — even those who consider themselves to be masters of the weight room in a gym find themselves struggling when they've been pulsing with a 1.5kg dumbbell for 45 seconds.

The weights may be light, but the burn is real. Define.London

"I love seeing clients blown away by the massive burn that happens when doing huge reps with such light weights," added Verma, who trains all her clients — including Victoria's Secret model Lorena Rae and TV presenter Lisa Snowdon — with 1kg or 2.5kg weights.

"It's beyond challenging and my clients see defined, sculpted results quickly. You can still get stronger by using lighter weights, just in a more all-over body way."

Verma is an advocate of the low-weight, high-rep approach because she believes it's beneficial for ensuring our longevity, too.

"As we age, we can develop joint problems and this can also be exasperated by the wrong kind of training," Verma explained. "Using lighter weights and incorporating longer reps will only empower the body, not hit it abruptly."

Lifting heavy will help you build strength

If you want to build bulging muscles, however, lifting heavy is the way to go, which means choosing weights so heavy you can't do very many reps at a time.

"Higher loads and lower reps produce strength gains," explained Worthington, a former international athlete whose celebrity client list includes world champions across a number of disciplines, models such as Winnie Harlow, and performers and dancers from leading shows in London's West End, New York's Broadway, and the Las Vegas strip.

"So think multiple sets of low reps – 5-6 sets of 3-4 reps might be common for someone looking to run faster or jump higher," he told INSIDER.

Resistance training needn't mean picking up weights, as Luke Worthington shows with TRX. Luke Worthington

However, this doesn't mean that by lifting heavy you'll immediately start resembling a body-builder, and, as Worthington points out, you'll only build muscle if you're in a calorie surplus — ie. consuming more energy than you're burning.

If your goal is simply to improve your body composition, Worthington recommends performing 3-4 sets of 8-12 reps per exercise — you need to choose a weight that allows you to do that, but also feel pushed.

Unlike Rein and Verma, Worthington does not advocate training with very light weights for excessively high reps.

"There isn't really any benefit to this outside of technique practice or in the early stages of post-injury rehab," he said.

"Building endurance isn't really something that's done in the gym — runners get better at running by running. That's where they get their muscular endurance. In the gym they train for strength to make them robust enough to do the running, and to reduce injury.

Luke Worthington

"Aesthetic changes are, broadly speaking, about reducing body fat in relation to lean tissue, so aim to produce a hypertrophy response whilst manipulating calories (surplus to gain muscle, deficit to lose fat)."

For this hypertrophy response, you need to be lifting heavy enough weights.

What does the science say?

In 2012, a study by McMaster University was undertaken to compare the training effects of light weights to heavy weights in young men.

The researchers tested the effects of performing leg extensions with either light (30% of 1 rep max) or heavy (80% of 1 rep max) weights over a 10 week period.

Interestingly, the researchers found that both heavy and light loads increased muscle size equally.

According to Alexander J. Koch, PhD, CSCS, USAW, who is a professor and program coordinator for exercise science at Lenoir-Rhyne University, the key is that both loads were lifted to exhaustion.

"That means the 80% group was lifting a weight that made them fatigue after about 10 repetitions, while the 30% group was lifting weights that tired them out after about 35 repetitions," he explained to INSIDER.

"What this tells us is that, as long as each set is taken to muscular fatigue, the load lifted isn't as important as the maximal effort applied for building muscle. This is because all muscle fibers will be recruited as a load is repeatedly lifted to failure."

Working to fatigue is key. Define.London

While the researchers found both techniques were equally efficient at building muscle, they also discovered that for building strength, the 80% load produced superior results.

"For building strength, it is better to lift heavier weights because the heavier loads train your nervous system to be able to recruit more of your muscle cells to produce more force more quickly, something that a light load will not duplicate," Dr Koch explained.

"A really important point is that the similarity between different loads was seen in this study was only because every set in both conditions was lifted to muscular failure. This is really brutal training beyond what most people would be willing to endure long term.

"So in general, one would be most likely to realize the best benefits of muscle and strength-building by repeatedly lifting heavier loads (80%+) to the point of near-fatigue (6-10 reps, but leave a little something in the tank) over time, as this could be done with a much lesser likelihood of inducing burnout."

There are pros and cons of both

There are undeniably pros and cons to both ways of resistance training.

"Training with low weight and a high number of reps generally means a shorter recovery period between workouts, along with shorter rest periods between sets," Hannah Bright, a British nutritional adviser and certified personal trainer at DW Fitness First, explained to INSIDER.

"The number of calories burned is likely to be higher and there's less pressure on joints."

A post shared by HANNAH BRIGHT - WELLNESS (@hannahbrightwellness)Mar 2, 2019 at 11:34pm PST

Bright went on: "On the flip side, training this way is likely to take longer to build bigger muscle and you're not likely to improve your strength massively. Whereas when lifting a higher weight with lower reps, you'll definitely see your strength improve, along with bone density and a greater fat loss.

"The cons of this type of training are that you'll need a longer recovery period for the muscle group in training, your workout is likely to be longer, and you're placing joints under a lot of stress."

How to get results from your weight training

Which training method you choose really depends on what you're hoping to achieve, what works for you, and just what you enjoy.

What's key, however, is that you create what's known as progressive overload — this means either increasing weight volume or number of reps over time.

"I set a general rule with my clients of an increase of no more than 10% per week in load or volume (never both)," Worthington said. "This tends to mean we still have something to aim for in the next session whilst minimising injury risk.

"However, progression will not always be linear — there is a point at which you will not be able to perform more reps or add more weight."

Both heavy and light weights will help you build muscle. Luke Worthington

Ultimately, training with either light or heavy weights is going to be beneficial, or you can mix it up by incorporating both into your regime. Just make sure you work hard enough that your muscles start to fatigue.

"The most important thing is the understanding that resistance training is the key to pretty much every training goal," said Worthington.

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