A Muscle Primer
What you need to know about muscle to stay healthy for life
If you want to manage your blood glucose levels, keep your insulin working well, and stay healthy throughout your older years, focus on keeping and gaining muscle mass. It is also one of the most important things to maintain in order to live well and independently as you age. In other words, you can't afford to lose your muscle mass if you want to live long and well—with or without diabetes.
What exactly is muscle? It's about 20 percent protein, with the rest mainly made up of water plus a few minerals and some carbohydrate and fat stores. Human muscle is thought of having two types of muscle fibers, slow twitch and fast twitch, which refers to the speed at which the muscle can contract and be ready to contract again. Fiber speed determines whether they're good for doing long, slow endurance exercise (slow twitch) or explosive power activities like sprinting (fast twitch).
Muscle fibers actually exist on a continuum from slow to fast twitch for speed and from oxidative to glycolytic in terms of the energy that they use, and specific exercise training can make them change some of their speed and metabolic capabilities (1). No matter what activity you do, they are recruited in a step-wise fashion, meaning that the harder an activity becomes or the more power or force you need to produce, the more fibers get recruited overall. However, how they're recruited is well defined: You start with the slower ones since they're hard to fatigue—which is good since they're in postural muscles—and then add in the faster fibers as needed to produce more power or speed.
Even though they're really a mix, muscle fibers are still currently categorized into three types in humans: slow oxidative (SO, or Type I), fast, oxidative glycolytic (FOG, or Type IIa), and fast glycolytic (FG, or Type IIx). The Type IIb fibers we used to think that humans had only exist in lower mammals like rats apparently; we have Type IIx instead. Oxidative fibers can use a variety of fuels during activities, including carbohydrates, protein and fat, which is why they're recruited for doing activities lasting longer than two minutes. Glycolytic fibers primarily use glycogen (stored carbs) readily available in muscle and other compounds in muscle like ATP (the direct energy currency for all muscle contractions) and creatine phosphate that can only fuel activities for 10 seconds or less; accordingly, these fibers are only adequately fueled during shorter activities (30 seconds to two minutes) or bursts of speed or power.
To be honest, the muscle fiber types you have (or don't have, based on genetics) are not nearly as important as regularly recruiting as many of them as possible when you train. As you age, over time you lose the muscle fibers that you don't use. Since it's unusual for older individuals to sprint or lift heavy weights, natural losses of muscle include more of the faster twitch fibers that are normally used to produce power and speed. Of course, that means that you are also losing some of your strength over time, which can make it harder to do ordinary things or even basic self-care.
Recent research has shown that muscle soreness is not required for muscle and strength gains (2). Although any type of training can cause repetitive (overuse) injuries if done excessively or with poor form, most injuries are preventable. What's more, any type of training that increases the risk for spine injuries in particular should be undertaken with much care and adequate precautions to prevent injuries (3). Back problems are certain to limit your ability to train, but having to stop training altogether when doing any type of exercise due to injuries is a sure-fire way to lose muscle mass and should be avoided at all cost.
When it comes to diabetes management, maintaining your overall muscle mass leads to greater glucose uptake and storage in muscle as glycogen. Muscles have a limit to how much they can store, and having more muscle mass results in a greater potential storage capacity, whereas losing muscle mass through aging and disuse limits it. While aerobic activities like walking may not enhance your muscle mass as much due to their lower intensity, improvements in fitness levels are not necessary to experience enhanced metabolic and diabetes control, as long as you do the activity regularly (4).
In closing, do whatever you can to keep as much muscle as you can as you age, but avoid getting injured. Stay regularly active, do resistance training, and eat adequate amounts of protein and calories. Your good health well into your later years will be your reward!
Please visit www.diabetesmotion.com for more helpful information about being active with diabetes.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
- (1) Ingalls, CP. Nature vs. nurture: can exercise really alter fiber type composition in human skeletal muscle? J Appl Physiol, 97(5): 1591-1592, 2004 (http://jap.physiology.org/content/97/5/1591)
- (1) Flann KL, LaStayo PC, McClain DA, at al. Muscle damage and muscle remodeling: no pain, no gain? J Exp Biol. 214(Pt 4):674-9, 2011 (http://www.ncbi.nlm.nih.gov/pubmed/21270317)
- (1) Hak PT, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. Nov 22, 2013. [Epub ahead of print] (http://www.ncbi.nlm.nih.gov/pubmed/24276294)
- (1) Pandey A, Swift DL, McGuire DK, et al. Metabolic effects of exercise training among fitness-nonresponsive patients with type 2 diabetes: The HART-D study. Diabetes Care. 38(8):1494-501, 2015 (http://www.ncbi.nlm.nih.gov/pubmed/26084342?dopt=Abstract)
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