Preface: I have consistently trained legs at least twice a week for the past 2 1/2 years – squats, leg presses, curls, extensions, lunges – you name it! And which of my muscle groups is probably the smallest/weakest? My legs. Those massive quads and shapely hamstrings – NOPE – NOT ON ME. But what I can offer instead – despite training less but somehow increasing in strength and size month over month – is a whole lotta upper body: back, shoulders, and traps (Yes – Traps – On a girl).
(Actual photo taken of me in shorts.)
So what gives????? Something you probably don’t want to hear. Your genetics!!
Recent research has shown that some individuals respond VERY well to strength training, some BARELY respond, and some don’t respond AT ALL. Yes. You heard that right – DON’T – RESPOND – AT – ALL.
A landmark study by Hubal used a total of 585 male and female subjects and showed that after 12 weeks of progressive dynamic exercise – the results were.. well…. the results were splattered across a WIDE range of responses – to say the least. UNDER THE EXACT SAME TRAINING PROTOCOL – The WORST responders LOST 2% of their muscle cross-sectional area and didn’t gain ANY strength whatsoever and the BEST responders INCREASED muscle cross-sectional area by 59% and INCREASED their 1 rep max strength by 250%. (These guys won the genetic lottery.)
Sooo.. um…. yeah.. what the heck right??? Let’s take a closer look at how genetics plays a role in all of this and hopefully dig up some answers……
Muscle Fiber Distribution
Muscles contain an assortment different fibers, namely Type I fibers that are “slow twitch” fibers and Type II fibers that are “fast twitch” fibers. Slow twitch fibers use oxygen to fire (are aerobic) and take longer to get going – but once they do, can go for a long period of time without getting tired. Because of this, slow twitch fibers are more endurance oriented. Fast twitch fibers fire without oxygen (anaerobically) and fire extremely fast but get tired easily. These fibers are the ones used when lifting weights. (Want to know more about how your muscles fire and use energy? – Check Out: Take it from a Chemist: Cardio Before or After a Workout? (Part 1 – The Science!) ) Based on your genetics, you can have more of one type of fiber than another type AND you may even have more of one type than the other in just the different parts of your body. Although both types of fibers can increase in size through weight training over time, fast-twitch fibers exhibit a greater capacity for growth. For example, a person may have a greater ratio of fast-twitch to slow-twitch fibers in his or her lower body – creating bigger and faster leg-muscle growth (obviously not in my case).
Genetically Determined Body Type
Although you can change your physical appearance with diet and exercise, your genetically determined body type regulates your overall body composition. For example:
- Ectomorphs are characterized by being slim and linear with long and thin muscles/limbs and overall low fat storage
- Mesomorphs are characterized by having solid torsos, low fat levels, and wide shoulders with a narrow waist, they are naturally more muscular and hypertrophy (grow muscle) quickly
- Endomorphs are characterized characterized by increased fat storage, a wide waist and larger bone structure, they possess an overall round shape with greater fat distribution
Ectomorphs are not predisposed to store fat nor build muscle. Mesomorphs are predisposed to build muscle but not store fat. AND Endomorphs are predisposed to storing fat.
Anabolic (muscle building) hormones regulate hypertrophy. Although weight lifting increases anabolic hormone circulation throughout the body, women (after all – gender a genetic trait) naturally posses lower levels than men, which is why women do not have the capacity to grow muscle the way men do (see photo below). The amounts of human growth hormone and insulin-like growth factors (two more anabolic hormones) also vary between individuals AND are influenced by training status AND genetics. (For more information on hormones, lifting, and women – Check Out: Fitness Myths – Episode 4 – Men & Women Should Train Differently and Hormones 101)
So when you boil it down – Genetic factors influence the rate and amount of muscle growth for each and every one of us. Muscle growth is influenced by muscle fiber type, fat distribution/body type, individual hormone levels and the overall quality and length of your weight training program. Although you cannot change your genetic makeup, you CAN design a routine that will lead you on the path to success. Your workouts have to be individually designed and fit your needs perfectly. If you want to develop your full potential you have to follow the routine that gives the best results FOR YOU.