Miller JZIf you have any physiology, performance, or nutrition related questions, email Ben at

 The weaker sex? – Part II

In the last column I discussed the small differences in energy metabolism between males and females.  In this column, I will focus on the making of protein, or more specifically, the making of muscle protein.


Most of the structural components of cells and tissues are proteins.  The total sum of proteins in your body largely dictates your body type (phenotype).  Skeletal muscle is the largest “pool” of protein in your body, which is why meat (animal muscle) is high in protein.  The existence of a protein is largely determined by two opposing processes – protein synthesis (the making of protein) and protein breakdown.  If protein synthesis exceeds protein breakdown, you add proteins; if protein breakdown exceeds protein synthesis, you lose proteins.  


When people think about adding muscle mass, they are really adding protein mass.  Adding muscle mass after weightlifting is due to the making of contractile proteins, which cause the muscle to get bigger.  Although this is an example in which your muscle gets bigger, there are many more examples where you add proteins without getting bigger.  For example, as an endurance athlete, you want a lot of mitochondria to produce energy to sustain prolonged periods of high work rates.   Mitochondria are essentially big bags of proteins.  Thus increasing the making of mitochondrial proteins, which does not necessarily result in big muscles, is a very important adaptation.   



There are two main ways of stimulating the making of protein in muscle. The first is adaptation to a stimulus (e.g. physical activity) the second is by feeding protein.  Regarding feeding protein, this works because your skeletal muscle essentially acts as a storage reservoir for dietary protein.  Your skeletal muscle is the first to add protein when it is consumed, and it is the first to lose it when you are hungry (hence muscle wasting during starvation or loss of muscle when dieting).  A point of caution here that is almost never heeded by the muscle heads of the world; eating protein to add muscle only works to a certain extent before you just start peeing out the protein that you take in (making expensive urine).  


With this background, and the knowledge that men in general have a larger muscle mass than women, it seems as though protein requirements may differ between men and women. I’ve been involved in a series of studies looking at whether there are sex differences in the factors that stimulate protein synthesis in skeletal muscle.  If we consider adaptation to exercise, it appears that men and women respond to a given bout of exercise with the same increases in protein synthesis.  If we consider feeding, it also appears that the increase in protein synthesis is equal in males and females.  These findings of no differences led to further investigations trying to tease apart the nuances that contribute to the differences in muscle mass between the sexes.    As with energy metabolism, measurements of protein synthesis were made at different times within the menstrual cycle as well by manipulating oral contraceptives (attempting to tease out the effect of female hormones). Again, these studies were largely unable to detect differences between men and women.  


Recently our lab thought about the fact that many of the measurements of protein synthesis were done over a very short time period; and perhaps what we see manifested as a difference between men and women are the result of very small (as to be undetectable) differences over a long period of time.  To answer this question, we used new methods designed to make measurements over 4 weeks to hopefully be able to accentuate differences in protein synthesis between men and women.  In what was a little bit of a surprise, we found the first real differences between men and women in the making of protein.  In this study, we found that during an exercise-training program, men made more protein than women.  Although this is an interesting finding (and yet to be published) there is one important caveat.  For this study we use a high-intensity sprint-interval training program, which is a unique type of exercise.  During the exercise training, males were able to reach higher workloads (more watts) on their sprints and performed greater total work.  However, when we scaled the work to how much muscle mass the males and females had, there was no difference in the amount of work per gram of muscle mass.  Therefore, it is unclear whether total work, or work per gram of muscle is the important factor to stimulate making more protein.  As I stated, this is the first documentation of a sex difference in protein synthesis.  If we apply our methods to other forms of exercise, or feeding, or just resting, it would be interesting to see if we could capture similar differences.  


With this study, we have documented that there is the potential that men and women adapt differently to different types of activities.  There is a whole body of literature (that I did not go into) documenting other differences in men and women. For example, there is a very compelling body of literature that indicates that women are more fatigue resistant then men, which is often the counter to the ability to produce very high peak forces (thus limiting women in our high-intensity protocol).  For now, let’s just state that men and women may be more adaptable to different types of activities and perhaps a fruitful area for applying this information is to not treat men and women the same when training them.  In other words, we should not expect women to perform the same way as men in that they could be better than men at some things while men may be better at others.  Further, if a male or female want to train to accentuate their strengths, there may be differences in how the training stimuli to do so.  As you may notice, I have put “may” in everywhere since none of this is tested and is just my speculation.  


In conclusion, women are not the weaker sex, rather men and women are just subtly different and perhaps should not be treated the same.  In my mind, the best way to apply this is to not pigeonhole women into the same training programs than males (which is typically the case).  Rather, one should consider women to be distinct and subject to their own style of training.  What that training style should be is yet to be explored.