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Research on Muscle Mass in Men vs Women states that; Dawn Yoerger Anatomy and Physiology Keiser University Prof. Popp 3/23/2023 Research The word ‘muscle,’ which means “little mouse,” has one main purpose: to convert chemical energy (ATP) into motion and movement (Saladin 2020; pg. 300). Muscles make up almost 50 % of the human body’s weight and are studied for many reasons in the medical field and fitness arenas (Saladin 2020; pg. 300). One studied area is the difference in men’s skeletal muscle mass vs. women’s skeletal muscle mass. Studies have shown there are over 3,000 genes that are expressed in male and female skeletal muscle differently (Haizlip et al; 2015). One difference is in the type of muscle fibers found in men versus women. There are two types of muscle fibers, Type I and Type II. Type II fibers are also called fast-twitch fibers or Fast Glycolytic (FG) fibers. These fibers play a part in quick reflexes and motility (Saladin 2020; pg. 407). Men typically have more of these fibers, which contribute to greater power output (Williams 2019). Type I fibers are also called slow-twitch fibers or slow oxidative (SO) fibers and are suited for endurance maintenance and fatigue resistance (Saladin 2020; pg. 407). Women have more Type I fibers which allow for greater capacity for recovery (Williams 2019). In a study of 468 men and women aged 18-88 years, the use of magnetic resonance imagery (MRI) provided accurate measurements and solid evidence to support the statement that men have more muscle mass than women (Janssen et al; 2000). Men showed to have more upper body skeletal muscle (SM) than women, whereas women had most of their muscle mass accumulated in their lower body (Janssen et al; 2000). While women carry most of their muscle in their lower half, men still have an overall higher percentage of SM compared to women; 36% more muscle mass than women (Janssen et al; 2000). Even in terms of body fat percentage and what is necessary for survival, women need 10-13% compared to just 2-5% needed for men (Maloney 2019). In fit and athletic women, their body fat percentage is typically 14-24%, compared to 6-17% of athletic men (Maloney 2019). While 10-13% is necessary for survival, it can disrupt hormonal function and result in amenorrhea, which is the absence of menstruation (Maloney 2019). This can be observed in many elite adolescent female athletes, who do not have a high enough body fat percentage to begin or maintain menstrual cycles. Without menstruation, this can cause fertility issues. This is another reason that women are genetically designed with more body fat and less skeletal muscle compared to men. In an interesting 2016 study on men and women aged 65 and older, they spent 18 weeks doing resistance training, and the results showed both genders had muscular gains, but men had bigger gains in muscular mass and maximal torque (Maloney 2019). Sarcopenia, which is a decline in SM, occurs more frequently in women under 70 and in men over 80 years old (Maloney 2019). This is primarily caused in women by lack of estrogen as they experience menopause. It is important for women to continue weight-resistance training to build bone density to counteract the effects of estrogen loss (Maloney 2019). In conclusion on Research on Muscle Mass in Men vs Women, it is scientifically proven that men are physically and genetically built differently and have more muscle mass than women. Critical Thinking This topic has intrigued me for a while, especially in recent years with the rise in transgender athletes in professional and Olympic sports. Despite the rise in estrogen and drop in testosterone as athletes transition genders, is it enough to make a difference in performance to keep a fair playing field? More research will have to be conducted, but I believe that given the studies on men and women genetically and SM comparison, there is still an unfair advantage to transgender women versus cis women in professional sports. WC 513 References Haizlip KM, Harrison BC, Leinwand LA. Sex-based differences in skeletal muscle kinetics and fiber-type composition. Physiology (Bethesda). 2015 Jan;30(1):30-9. doi: 10.1152/physiol.00024.2014. PMID: 25559153; PMCID: PMC4285578. Janssen I, Heymsfield SB, Wang ZM, Ross R. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr. J Appl Physiol (1985). 2000 Jul;89(1):81-8. doi: 10.1152/jappl.2000.89.1.81. Erratum in: J Appl Physiol (1985). 2014 May 15;116(10):1342. PMID: 10904038. Maloney, L. (2019) Amount of muscle mass in men versus women | livestrong, LIVESTRONG.COM. Leaf Group. Available at: https://www.livestrong.com/article/246036-how-much-more-muscle-mass-does-a-male-have-than-a-female/ (Accessed: March 23, 2023). Williams, T. (2019) Muscular strength in women compared to men | livestrong, LIVESTRONG.COM. Leaf Group. Available at: https://www.livestrong.com/article/509536-muscular-strength-in-women-compared-to-men/ (Accessed: March 23, 2023). Saladin, K. (2020). Anatomy & physiology: The unit of form and function (9th ed.). McGraw Hill Education.
