You've heard so many people talk about it before.
"It's just his/her genetics" they say.
But just how important are genetics for muscle growth and fat loss?
You might be surprised to learn that there's a lot more to genetics than just how we respond to training.
Believe it or not, we can hold them accountable for our motivation to exericise as well!
We'll get to genetics and muscle growth later (which will blow your mind).
But the first interesting concept is that genetic/biological factors play a role in our activity levels.
Research (1) has discovered that the genes called dopamine receptor 1 (Drd1) and nescient helix loop helix (Nhlh2) are "excellent candidate genes for the regulation of physical activity".
Essentially, some of us are more motivated to get out there and get active than others.
Researchers are currently working on discovering the other genes that play a role in our motivation to get off the couch.
However, studies on mice and the above mentioned Nhlh2 tell us that when this gene is strategically removed, it leads to "adult-onset obesity and reduced physical activity" (2).
It's led the above cited researchers to hypothesise that this gene is an important factor in the motivation AND ability of exercise.
And this is all BEFORE we start comparing how we respond to the exercise we do.
GENETICS AND YOUR WAISTLINE
Research is clear that our risk of developing obesity has a "significant genetic component" (3).
However, researchers are still not certain on exactly what genetics are behind human obesity (3).
Currently, because all the genes are still being discovered, there's no solid explanation for this.
It isn't as black and white as you might think.
Research into weight loss conducted on identical females twins has found "a strong genetic contribution" (4).
In this study, subjects were studied for 40 days in three phases: 7 baseline days; 28 days of weight reduction by a very low calorie diet and 5 days after weight reduction.
While there was huge variability among the pairs in weight and fat loss, the correlation WITHIN the twin pairs was very similiar.
This suggests that although the seperate groups of twins lose weight at different rates, the two in the same group report similiar results and metabolic effiency.
It's why these researchers suggest a "strong genetic contribution" to weight loss - a claim also backed up by many other reseachers in this area of today's scientific literature.
Further research (5) into more twins (this time 12 pairs) involved over feeding them by 1000 calories everyday for 84 days over a 100 day period.
This is a total of 84,000 excess calories!
Those taking part in the study maintained a completely sedentary lifestyle during the research.
The average weight gain was 8kg - but incredibly, the range was from 4.3kg - 13.3kg!
What's interesting here is that the luckiest individual with the best genetics stored just 40% of the excess calories in his tissues, whilst the unluckiest person stored 100% of the calories.
And further data (6) from the same group of researchers found similiar results in identical twins, even when they were exercising regularly.
This work from these researchers has led them to guess that 40% of the variability in your thermic effect of food, your resting metabolic rate and your number of calories burnt during low-to-moderate intensity exercise is genetically related.
They don't call it the genetic "lottery" for no reason!
More research (7) shows that your mum and dad are responsible for 42% of your subcutaneous fat and 56% of your abdominal visceral fat.
Genetics really do greatly influence where your fat is stored.
You've probably noticed some people seem to store all their fat in their abdominal region - well this is why!
GENETICS AND YOUR MUSCLE GROWTH
One study shows just how vital genetics are for muscle growth (8).
In this set-up, 585 male and female subjects lifted weights for 12 weeks in a progressive fashion.
Some increased muscle cross-sectional area by a jaw dropping 59% - and increased their 1RM (1 REP MAX) by 250%.
And the others?
They LOST 2% of their muscle cross-sectional area and as far as strength went - they didn't improve at all!
And remember, both groups did the SAME workouts.
Further research (9) looked at 66 human subjects who underwent 16 weeks of progressive dynamic exercise.
At the end of the study, 26% of the participants walked away without any measurable growth.
Put simply, your muscles can't grow unless the satellite cells surrounding their fibers pass on their nuclei to your muscles in order to produce more genetic material to signal the cells to grow.
The above cited study showed that satellite cell activation was the difference in the responses.
The better responders have MORE satellite cells that surround their muscle fibres, and better yet, a crazy ability to make their satellite cell pool even BIGGER by training!
Know a guy who trained for a few months and responded amazingly?
This is one of the reasons.
The excellent responders averaged 21 satellite cells per 100 fibers at baseline, which increased to 30 satellite cells per 100 fibers by week sixteen, which resulted in a 54% increase in mean fiber area.
And as for the non-responders - they averaged just 10 satellite cells per 100 myofibers at baseline, which sadly didn't change post-training.
Genetics play a huge role in our training when it comes to motivation, muscle growth, fat loss, how we respond to a calorie surplus/deficit and even down to where we store our body fat.
Although many facets of genetics relating to fitness and body composition are still being discovered, we know enough to make an informed guess on our progress following similiar training/weight loss protocols to the ones cited above.
And if results aren't coming at the speed you'd like, tell your mum and dad I gave you permission to blame them!
"Stay Fit, Stay Flexed!"
(1) Lightfoot JT. Current understanding of the genetic basis for physical activity. J Nutr. 2011 Mar;141(3):526-30. doi: 10.3945/jn.110.127290. Epub 2011 Jan 26.
(2) Good DJ, Coyle CA, Fox DL. Nhlh2: a basic helix-loop-helix transcription factor controlling physical activity. Exerc Sport Sci Rev. 2008 Oct;36(4):187-92. doi: 10.1097/JES.0b013e31818782dd.
(3) Kowalski TJ. The future of genetic research on appetitive behaviour. Appetite. 2004 Feb;42(1):11-4.
(4) Hainer V, Stunkard A, Kunesova M, Parizkova J, Stitch V, Allison DB. A twin study of weight loss and metabolic efficiency. Int J Obes Relat Metab Disord. 2001 Apr;25(4):533-7.
(5) Bouchard C, Tremblay A, Despres JP, Nadeau A, Lupien PJ, Theriault G, Dussault J, Moorjani S, Pinault S, Fournier G. The response to long-term overfeeding in identical twins. N Engl J Med. 322(21):1477–1482, 1990.
(6) Bouchard C, Tremblay A, Despres JP, Theriault G, Nadeau A, Lupien PJ, Moorjani S, Prudhomme D, Fournier G. The response to exercise with constant energy intake in identical twins. Obes Res 2:400–410, 1994.
(7) Perusse L, Despres JP, Lemieux S, Rice T, Rao DC, Bouchard C. Familial aggregation of abdominal visceral fat level: results from the Quebec family study. Metabolism 45:378–382, 1996.
(8) Hubal MJ, Gordish-Dressman H, Thompson PD, Price TB, Hoffman EP, Angelopoulos TJ, Gordon PM, Moyna NM, Pescatello LS, Visich PS, Zoeller RF, Seip RL, Clarkson PM. Variability in muscle size and strength gain after unilateral resistance training. Med Sci Sports Exerc 37: 964–972, 2005.
(9) Petrella JK, Kim JS, Mayhew DL, Cross JM, Bamman MM. Potent myofiber hypertrophy during resistance training in humans is associated with satellite cell-mediated myonuclear addition: a cluster analysis. J Appl Physiol 104: 1736–1742, 2008.