The Fun Science of Female Muscle
When T Nation first launched, we spent a lot of time trying to convince women to pick up heavy things. Back then, there were a lot of myths out there. Today, more women than ever are lifting. Maybe we helped. And luckily, science too has turned its microscopes on female muscle and nutrition.
Here are six quick study summaries for women who lift and men who love women who lift. (Note: Most of this info comes from T Nation contributor Bill Campbell, PhD. I'll be quoting him liberally.)
The speed of your metabolism is largely dependent on your overall size. Bigger people usually have higher resting metabolic rates (RMRs). But as Dr. Bill Campbell notes, there are other variables involved.
In a study of male and female endurance athletes, the best predictor of RMR in men was muscle mass. We expected that. But in women, the best predictor was calorie/food intake (1). In short, women with the highest metabolisms ate a lot and trained a lot. They lifted weights, they did cardio, and they were not shy at the dinner table.
Dr. Campbell warns, "A good way to slow down your metabolism is doing the opposite – reducing your calories and not exercising!" Sounds like the typical frustrated yo-yo dieter, doesn't it?
You may have heard this referred to as "energy flux." It basically means taking in a lot of calories and then frequently expending a lot of calories through exercise: eat a lot, train a lot.
This should hammer another nail into the "starvation and cardio" coffin. The best female metabolisms, and the best-looking bodies, are built through eating plenty of healthy food, lifting lots of barbells, and doing conditioning work.
Think of the top female CrossFit athletes: They train a lot in a variety of ways. And while most of them make healthy food choices, they certainly don't adopt low-calorie diets. The result? High-performance bodies, blazing-fast metabolisms, and leanness.
Based on seven published case studies, the average female who enters a physique competition has to lose about 17 pounds – or 11% of her body weight – to be stage-ready. The average male needs to lose about 27 pounds. This is a rough average, of course, but interesting nonetheless.
I'm not sure about women, but men typically underestimate how much fat they need to lose to compete. The average dude thinks he's 10-15 pounds away from being ripped. According to this study at least, it's often double that. (Let's also keep in mind that "stage-ready" isn't often sustainable or even healthy.)
Related, for a woman to have a visible 6-pack, her body fat percentage needs to be around 10-11% as measured by skinfolds or ultrasound. As Dr. Campbell reminds us, trying to maintain 6-pack abs all year long isn't healthy for the vast majority of women.
In a study conducted in Dr. Campbell's own Physique Lab, women were divided into two groups:
- One group added 250 calories to their diets, all from protein.
- One group dropped 300 calories from their diets, all from protein.
After 8 weeks, the group that increased their calories and protein intake lost 2 percent of their body fat. The lower-calorie, lower protein group lost almost no body fat, maybe 1 percent (2).
Did you catch that? Women lost MORE fat by eating 300 more calories if those extra calories came from protein and they were lifting.
"This study impacted my view on protein intake," Dr. Campbell notes. "I used to think that if you increase calories, you'd gain fat. I still think this is generally true, but now I appreciate that if you increase your calories in the form of protein – and you're resistance training – it's possible to lose body fat."
If a 140-pound woman eats about 100 grams of protein per day, she'll maximize her muscle gains. That's roughly 0.75 grams of protein per pound of body weight. (3) (4)
As Dr. Campbell points out, the average woman may think this is a lot of protein. However, a dedicated female lifter may say the same thing the girl who took my virginity said: "That's it?"
In a nutshell, if a weight-lifting woman isn't getting enough protein to increase her muscle mass, bumping up to 0.75g/lb will do the trick. But several studies have shown that going past that number doesn't do much for muscle gains.
Does that extra protein "turn to fat?" Not necessarily; it may even decrease body fat if she's lifting. (2)
In fact, Dr. Campbell recommends women use the 0.75g/lb number as a minimum daily protein intake to look good naked. If you exceed that number a bit, don't expect further muscle gains, but it's not going to hurt either. That extra protein will probably keep you full longer and displace more fattening foods.
In a study by sports scientist Jason Cholewa, two groups of newbie women were put through the same three-day-per-week lifting program for 9 weeks. (6) However...
- One group used moderate loads and hit technical failure at 10-14 reps.
- One group used heavier loads and hit technical failure at 5-7 reps.
The result? Both groups gained almost exactly the same amount of muscle: 3.5 pounds.
This would lead us to believe that rep ranges just didn't matter much if the sets are intense – performed to failure (without losing good form) or darn close to it.
A few caveats:
These were all women new to resistance training. A more experienced female would probably want to spend time using all the effective rep ranges, especially if she wants to keep getting stronger.
Also, this was just a 9-week study. If you look closely at the "statistically insignificant" numbers, the moderate-rep group gained 3.5 pounds of muscle while the lower-rep group gained 3.3 pounds. Now, extend this study to a year or more. Those little fractions could add up to additional muscle.
But really, we're splitting hairs. The lesson here? All rep ranges can build muscle if that last rep is challenging enough. That's true for men too.
Three studies show that women who want to get stronger just aren't lifting heavy enough to accomplish their goals. (6) (7) (8)
To build maximal strength, a woman needs to lift greater than 85% of her 1-rep max. In these studies, when women were allowed to "self-select loads" or choose their own weights, both untrained and experienced women undershot that amount.
I doubt most of these women were sandbagging it out of laziness. My hypothesis: they were probably playing it extra safe or simply underestimating themselves. (Men typically do the opposite on both counts.)
Ask any good trainer, and they'll say their female clients can usually hit a 5-rep target with more weight than they would've guessed. Most women are stronger than they think.
Note: Give Dr. Campbell a follow on his Instagram. Lots of great info like this there.
- Thompson M. Predicted and measured resting metabolic rate of male and female endurance athletes. Am Diet Assoc. 1996 Jan;96(1):30-4.
- Campbell BI et al. Effects of High Versus Low Protein Intake on Body Composition and Maximal Strength in Aspiring Female Physique Athletes Engaging in an 8-Week Resistance Training Program. Int Nutr Exerc Metab. 2018 Nov 1;28(6):580-585.
- Antonio J et al. The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals. J Int Soc Sports Nutr. 2014 May 12;11:19.
- Antonio J et al. A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women--a follow-up investigation. J Int Soc Sports Nutr. 2015 Oct 20;12:39.
- Cholewa JM et al. The Effects of Moderate- Versus High-Load Resistance Training on Muscle Growth, Body Composition, and Performance in Collegiate Women. J Strength Cond Res. 2018 Jun;32(6):1511-1524.
- Glass SC et al. Self-selected resistance training intensity in novice weightlifters. J Strength Cond Res. 2004 May;18(2):324-7.
- Focht BC. Perceived exertion and training load during self-selected and imposed-intensity resistance exercise in untrained women. J Strength Cond Res. 2007 Feb;21(1):183-7.
- Cotter JA et al. Ratings of Perceived Exertion During Acute Resistance Exercise Performed at Imposed and Self-Selected Loads in Recreationally Trained Women. J Strength cond Res. 2017 Aug;31(8):2313-2318.