It is also important to remember that you do not have to run a marathon or perform “traditional” exercise to be healthy. Did you know that even if you don’t go to the gym, swim, bike or run that you are still exercising everyday? Your activities of daily living (i.e. cooking, cleaning, going to work or school, chasing after your kids, or sitting at your computer) provides a training stimulus!!! Yes, you read that correctly, even the act of sitting upright, which is normally classified as a sedentary behavior requires muscle activation and on some level can be considered training. Technically, any movement performed against gravity is training! The training stimulus of sitting is quite small; however, compare and contrast the amount of muscle activation in a person sitting upright to someone who is bedridden or who is experiencing the microgravity of space.
Critically ill patients placed on mechanical ventilators (which do the work of breathing) lose diaphragm mass (the muscle responsible for breathing) within 18-48 hours of being placed on a ventilator (1,2). As little as 7 days of bed rest in otherwise healthy individuals causes them to lose 1-4% of their back and lower extremity muscle mass (3). Casting of the lower leg for 6 weeks after an ankle fracture can decrease lower leg muscle volume by ~17% (4). In each of these cases, the demand place upon the muscle decreased and so did the muscle volume. Use it or lose it!
In the microgravity environment of space as few as 5 days (and the loss of the stimulus of gravity, against which your muscles pull when you move) caused muscle cross sectional area, a measurement of muscle size, to decrease by as much as 24% in type II muscle fibers (5). The longer the space flight, the greater the loss of muscle size becomes (6,7). Again,Use it or lose it! Of course, these are extreme examples of disuse, but they serve a point as to how quickly physical inactivity can have negative health consequences.
So, whether you believe it or not, your daily physical activity is still training. The more daily movement you have, the more you are training. Stand up from your chair = training. Washing your hands = training. Walking to your car = training.
Figure 1: The Exercise Continuum from Bed Rest to Trained Athlete. ADLs = Activities of Daily Living
Bed rest and the microgravity of spaceflight are representations of our most sedentary, detrained states and are found on the far left side of the continuum (Figure 1). Activities of daily living (ADLs) keep you more towards the middle of the continuum. Performing more activities of daily living will push you towards the right side of the continuum but if you really want to be on the right side of the continuum you’ll need to perform traditional resistance training (e.g., weight lifting) or aerobic training (e.g., brisk walking/running).
Protein synthesis, the impetus behind bigger, more tone muscles and fit bodies, increases almost immediately after working out (3 hours after) and remains elevated for more than 24 hours in novice exercisers (during which time protein synthesis peaks at around 150% of baseline) (8). This is why exercising at least every other day is so important. If you exercise every other day, as soon as your rate of protein synthesis decreases, you can stimulate your muscles to increase in size again (Figure 2).
Figure 2: Muscle Protein Synthesis Increases Dramatically after a Single Session of Weight Training (8).
Starting a new exercise program also yields an excellent return on investment. As few as three exercise sessions (in 1 week) has been shown to increase muscle size (9) and in most individuals a noticeable increase in muscle size occurs in less than 3-4 weeks of training (10). Now, I know that not everyone is seeking an increase in muscle size. In fact, most women are scared of lifting weights because they are afraid their muscles will become too big. Contrary to anecdotal reports, women simply cannot bulk up to the degree their male counterparts do in response to resistance training (11). In women, resistance training will tighten and tone, not bulk and burden.
Nutrition is also very important to how our bodies look and how we feel about them. If we created a continuum for nutrition it would span from anorexia to normal to obese (with normal being optimal). In the interest of time (and your attention spans) we will not discuss nutrition in the amount of detail that we discussed exercise. In brief, when we consume too many calories we place a demand on our adipose (fat) tissue to store these calories. When we eat too few calories, now the demand shifts towards releasing those calories from the adipose to be burned in other tissues such as skeletal muscle. Our fat stores reflect whether we have been ingesting more calories than we are burning over a prolonged period of time. The more food we eat, the bigger our bodies will get. The converse is also true. The less food we eat, the smaller we get, sometimes to the point of unhealthiness, anorexia, and even death (Figure 3).
Figure 3: The Energy Balance/Nutrition Continuum. The amount of food we eat and the amount of energy we burn contribute to where we find ourselves on the nutrition continuum.
When we have the right mindset, when we know exactly what we are up against, and we know how the body works, we can design a plan to create the type of body we want to have. The human body is highly malleable. THIS IS A GOOD THING! You can work to shape it the way you want it by knowing that the human body is a “DEMAND DRIVEN SYSTEM”. If we increase the demand of our muscles, they get stronger/bigger/more tone. If we increase the demand from our fat stores by eating less, they get smaller. Everyone has a different idea of what is right for them, there is no one size fits all to what someone should look like, just like there is no one size fits all for where someone should sit on the exercise or nutrition continuum. The important thing is that you are aware of where you sit, and that you are happy with it.
When you understand that the body is a demand driven system and you know the elements that are causing the body to be too big, too small, or just about right, YOU ARE IN CONTROL OF YOUR BODY and YOU can manipulate it to fit YOUR DEMANDS.
Todd M. Weber PhD, MS, RD
- Grosu HB, Lee YI, Lee J, Eden E, Eikermann M, Rose KM. Diaphragm muscle thinning in patients who are mechanically ventilated. Chest. Dec 2012;142(6):1455-1460.
- Levine S, Nguyen T, Taylor N, et al. Rapid disuse atrophy of diaphragm fibers in mechanically ventilated humans. The New England journal of medicine. Mar 27 2008;358(13):1327-1335.
- Shangraw RE, Stuart CA, Prince MJ, Peters EJ, Wolfe RR. Insulin responsiveness of protein metabolism in vivo following bedrest in humans. The American journal of physiology. Oct 1988;255(4 Pt 1):E548-558.
- Psatha M, Wu Z, Gammie FM, et al. A longitudinal MRI study of muscle atrophy during lower leg immobilization following ankle fracture. Journal of magnetic resonance imaging : JMRI. Mar 2012;35(3):686-695.
- Edgerton VR, Zhou MY, Ohira Y, et al. Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. Journal of applied physiology. May 1995;78(5):1733-1739.
- Fitts RH, Trappe SW, Costill DL, et al. Prolonged space flight-induced alterations in the structure and function of human skeletal muscle fibres. The Journal of physiology. Sep 15 2010;588(Pt 18):3567-3592.
- Widrick JJ, Knuth ST, Norenberg KM, et al. Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres. The Journal of physiology. May 1 1999;516 ( Pt 3):915-930.
- Damas F, Phillips S, Vechin FC, Ugrinowitsch C. A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy. Sports medicine. Jun 2015;45(6):801-807.
- Ogasawara R, Thiebaud RS, Loenneke JP, Loftin M, Abe T. Time course for arm and chest muscle thickness changes following bench press training. Interventional medicine & applied science. Dec 2012;4(4):217-220.
- DeFreitas JM, Beck TW, Stock MS, Dillon MA, Kasishke PR, 2nd. An examination of the time course of training-induced skeletal muscle hypertrophy. European journal of applied physiology. Nov 2011;111(11):2785-2790.
- Ivey FM, Roth SM, Ferrell RE, et al. Effects of age, gender, and myostatin genotype on the hypertrophic response to heavy resistance strength training. The journals of gerontology. Series A, Biological sciences and medical sciences. Nov 2000;55(11):M641-648.