Which is better, heavy weights or light weights?

Thanks to the popularity of new workout trends like CrossFit, most women are no longer totally afraid of the strength area of the gym. However, superstition about “bulking up” still lingers in the female psyche, and if you walk into any commercial gym you will see rows and rows of women on the treadmills, ellipticals, and stationary bicycles, instead of in the weight room.

The truth is that it does take “heavy” weight training for women to sculpt strong, lean physiques. Why did I put the word “heavy” in quotes? Read on to learn more…

How does male and female physiology play a part?

First of all, women do not have to truly worry about bulking up because they lack the testosterone to actually pile on muscle. Our bodies are not genetically designed to be as bulky or as lean as men’s bodies. The bottom line is that if a man and a woman both began a weight training program that was similar in proportion to their respective strength capacities, they would see very different results. Men, thanks to evolution, are wired to “bulk up.” Also, to reiterate a former blog post, women also gain lean muscle mass, but due to female hormones, women carry a naturally higher body fat percentage and their muscles are not designed to become as large as the muscles of men.

So if you take the possibility of “bulking up” off the table…

How does the body respond differently to heavy and light weights?

This is slightly reductionistic, but the bottom line is that light weights are about endurance and heavy weights are about strength. However, both heavy and light weights will put on lean muscle mass. In fact, some studies would indicate that heavy and light weights put on the same amount of lean muscle mass, for both genders.

How is this possible?

Fatigue is fatigue. If you wear out a muscle during a workout, you are breaking it down slightly and allowing it (with rest) to rebuild bigger and stronger. You can fatigue a muscle or muscle group with light weights or heavy weights. The key is that heavy weights are more efficient.

If it takes three sets of 20 reps to fatigue a muscle with a light weight, but only three sets of eight reps to fatigue a muscle with a heavy weight, which exercise plan would allow you to finish up at the gym more quickly and get on with your day? It’s the difference between working out for an hour, or working out for 20 minutes.

But there is another difference between light and heavy weights that many people don’t know about…

What role does explosive movement play?

Explosive movements are the main characteristic of very advanced, heavy weight lifting that builds the type of muscle fiber known as “fast-twitch” muscles. Explosive movements are fast, dynamic, and use momentum. Fast-twitch muscle fibers tend to build overall bigger, leaner muscles than slow-twitch muscles (which are engaged by endurance activities such as light weight-lifting or long-distance steady state cardio).

Explosive “power” movements are the final stop on the weight training continuum. If you do not currently weight train, you should not jump into a program that immediately includes excessive jumping, throwing, slamming, or other fast movements that involve weight (bodyweight included). The danger of finding all of your workouts on YouTube is that you may not be finding an appropriate (or safe!) exercise for where you are on your individual fitness journey. Not everyone reaches the level of “power” (explosive movements) in their weight training, and there are no shortcuts in the world of exercise science. In fact, you can develop a perfectly well-rounded training program (and very athletic appearance!) by focusing on slow, controlled movements indefinitely.

However, power training is very useful and beneficial for those who have already built balanced muscles through stability and strength training, and are motivated to increase lean muscle mass. If you frequently lift weights (two or more times a week), you may be a candidate for power training. It is wise to work with a trainer when starting a new exercise program.

Speaking of “heavy” and “light”… what specific weights count as “heavy” or “light”?

Is there a standard definition?

What constitutes heavy weights or light weights is the exertion of the individual. A truly heavy weight would be one with which you could not complete more than 3-6 reps without having to stop to rest. A “light” weight is actually a weight with which you cannot complete more than 12 reps. Any weight that allows you to complete more than 12 reps without needing a break is extremely inefficient, if not altogether ineffective (depending on the situation). Technically, you can do 30 reps with a very light weight and you will gain lean muscle mass, but it is a waste of time compared to doing 8 reps at a challenging level. Also, when a weight is too light, women often stop before they are truly fatigued because of the inefficiency of the workout. In other words, it’s boring to lift the same 2-lb. dumbbell for 10 minutes.

What weights should I be using, if that’s true?

For many women who are new to strength training, the following dumbbell weights are appropriate for an upper body workout of 8-12 reps for 3 sets each (but you may need to tailor this list to your individual needs):

  • Bench Press – 30-40 lbs. total (15-20 lbs. per arm)
  • Shoulder Press – 10-15 lbs. per arm
  • Rows – 10-15 lbs. per arm
  • Flies (lying face-up on a bench) – 5 lbs. per arm
  • Reverse flies (lying face-down on a bench) – 5 lbs. per arm
  • Lateral raises – 5 lbs. per arm
  • Bicep curls – 10 lbs. per arm
  • Tricep extensions (overhead) – 10-15 lbs. (one dumbbell)

Remember at the beginning of the blog post, when I put “heavy” in quotes? It’s because most women think of “light” as 1-2 lb. dumbbells, and “heavy” as 8 lbs. or more. The reality is that, depending on the exercise, 5-8 lbs. needs to be the bare minimum of “light” weights, and in order to stimulate lean muscle growth, fat loss, and metabolism revving, you need to have dumbbells of 15-20 lbs. or heavier at your disposal.

By the way, many women overlook their own bodyweight as an extremely efficient source of “heavy” weight. If you think about 10-lb. dumbbells versus your own 120, 150, or even 200-lb. frame, incorporating plank, pushups, pull-ups (with assist) and dips (with assist) into your routine is extremely beneficial.

Remember, heavy weights equal lean, sexy muscle.

So if women can’t “bulk up,” why do I see huge female body builders?

The short answer is diet. While it is true that women who train for body-sculpting, muscle-building events have a training plan that is calibrated to an exact science, the secret to their bulk is the amount and type of calories that they eat each day, in addition to supplements.

If you eat less than 2500 calories a day and are not designing a meal plan that tracks your macros (fat, carbohydrates, and protein), it is impossible to build muscle on the scale of a female body builder. It’s simply not physically attainable without the calories.

So how does my diet affect my weight training?

If you are an average, healthy female gym-goer who is flirting with the idea of increased weight training, you will need to take a close look at your diet to ensure (a) that you do not put on lots of strong muscle that is invisible under fat and (b) to make sure that you are getting enough food, and the right kind of food, to sustain your training program without cuing your body to go into stress/starvation mode.

If you eat junk food frequently (at least once a day, or more than once a day), you will not enjoy the aesthetic rewards of a new and rigorous exercise program. You will get stronger, but the results won’t be physically visible. There will be a layer of fat over your muscles that actually makes you look bigger as you get stronger. Unless this is what you want (for some people, strength is more competitively important than aesthetics), you will need to get a handle on your diet so that you are eating the correct amount and type of food. This is individual to each person, and if you think you need help designing a food plan for yourself, there are many resources online, and most likely a nutritionist in your area who could help you with sports nutrition and fat loss.

On the other hand, if you have a “dieting” mentality (you are eating less than 2000 calories a day as a habit) and you do not increase your calories when you start weight training, you will struggle to see results. Your body will interpret the increased weight training as a negative stressor and will begin to hold onto fat and burn muscle instead. To build lean muscle mass and burn fat, your body needs to be satisfied that it has enough resources to “make babies,” as I like to joke. Female bodies are predisposed to retain fat reserves for pregnancy, and your body will defend these stores of fat preferentially to muscle unless you send your body the message that everything is OK. Reassure your body by eating plenty of healthy fats and and sufficient calories when you are weight training.


Heavy weights sculpt sexy, lean muscles. However, a healthy, balanced way of eating and a variety of cardio activities must also be part of your lifestyle for the best results.

Finally, remember: everyone is different. Hormones and genetics can also have an effect on body shape. When you start a weight training program and do it consistently with a diet that supports it, you are going to be the most fit version of you, not a replica of an actress or model that you emulate.

Be realistic about the results that you want, and the time it takes to achieve them. Most of all, avoid an “all-or-nothing” attitude that can result in disappointment after perceived failure or slow results.

Weight training is awesome for women! The results go far beyond aesthetic appearance, and lifting should be a part of every woman’s workout routine. Be patient, do your best, and get the help of a professional if you need it. Keep doing your cardio at the gym, but design a workout plan that involves weights and head over to the dumbbell area as well!

Do you live in New York City and would like to work with me? Shoot me an e-mail using the Contact Form, and I would love to meet in person!

Have questions? Leave me a comment below!

Rachel Trotta

I am a Certified Personal Trainer, Fitness Nutrition Specialist, Physique and Bodybuilding Specialist, and Women's Fitness Specialist. I live in New Jersey in the NYC metro area, and I coach clients online all over the world. As a trainer and health writer, my mission is to make healthy living sustainable for the average person. I’m also a wife, mom, nature lover, runner, avid cook, weightlifting aficionado, history nerd, travel addict, and obsessive podcast listener. Get in touch!

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