What Happens to Your Body When You Lift Heavy vs. Light Weights

Lifting weights and strength training — as a supplement to your regular cardio program — offers immense benefits. Weightlifting builds your muscles and endurance, boosts your metabolism, helps prevent disease and even improves your mood.

Yet, there are many opinions out there on what type of weightlifting you should be doing, so it can be hard to know what’s right. 24Life did the research, here you go …

Is heavy or light better?

A recent study, funded by Natural Sciences and Engineering Research Council of Canada, focused on 49 men who had been weight training for a year. Split randomly into two groups, one group lifted heavy (within 75 to 90 percent of their one-repetition maximum); the other group lifted light (within 30 to 50 percent of their one-repetition maximum). Each group was tasked with exhausting the muscle regardless of weight lifted.

For the heavy lifters, it took less reps to do so; for the light lifters, more reps. (You can read more about the results of that study here on 24Life.)

At the end of the study, all the participants had gained muscle strength and size — in fact their gains were almost identical. The key to gains was total muscle fatigue, not at all dependent on weight.

Pete McCall, science officer at the Institute of Motion, says “if fatigue isn’t achieved, not all fibers will be activated and engaged.” So choosing weights versus reps really comes down to preference.

If you prefer light weights and high reps …

What happens to your body: High reps increase your heart rate and produce a cardio effect to help burn calories and fat.

High reps build muscle endurance, which supports muscles while working under stress. This type of weight training can supplement endurance training — say if you’re training for a triathlon or marathon, for example.

As a bonus, high reps of light weight create “a greater amount of total work,” which maximizes the calorie burn, according to Well by The New York Times.

McCall adds that high reps create a metabolic demand on the muscle that depletes glycogen stores in the muscle. A result of high-rep training is the body may start storing more glycogen, increasing muscle size.

Moves to get results: McCall recommends these light-loaded, high-rep exercises —

If you prefer heavy weights and low reps …

What happens to your body: Heavy weights at low reps break down muscle fibers, and the body builds muscle and increases muscle mass by repairing these fibers. Increased muscle mass elevates metabolism, which helps your body continue to burn calories long after your workout.

Heavy lifting also strengthens bone density, which can reduce the risk of breaks and fractures as you age. If you lift heavy, you test your mental strength as well.

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Lifting heavy increases production of a brain-derived neurotrophic factor, the neurotransmitter related to producing new brain cells and improves cognitive function.
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Moves to get results: McCall recommends these heavy-loaded, low-rep exercises —

Why you should pursue variance regardless of preference …

Variance is key for optimal fitness. Although you may choose to lift light or heavy based on your goals and preferences, switching up your lifting routine and overall fitness regimen every once in awhile yields the greatest results. Through a non-routine or rotating diverse routines, you can help prevent a plateau.

Switch from light weights to heavy weights in the weight room or check out a fitness class that focuses on core and strength training. Yogis may even integrate weight training into their yoga practice using dumbbells as a full-body workout to sculpt muscles.

Varying workouts (and even adding in outdoor activities or sports) may maximize your fitness, but it also keeps you motivated and challenged. If boredom begins to override motivation, your workouts and health suffer.

So, pick up a heavy barbell and light free weights, lift at low and high repetitions. The answer in the great weight debate between heavy and light is simply: do both.