Have you been diagnosed as a Type II Diabetic, and wondering why you have suddenly become exhausted when performing certain tasks? This is true, especially when it comes to exercising. During an intense bout of exercising healthy individuals will notice their ability to train at a high intensity begins to diminish roughly between 30 to 45 minutes of participating in vigorous exercising. When conducting moderate training a healthy person can sometimes sustain 60 consistent minutes of exercising before they are met with a reduced ability to perform in the gym.
This reduction is commonly referred to as fatigue. Fatigue will cause our motor units to reduce contractile potential, recruitment, and maximal force capacity (2). Simply put, motor units work to stimulate our muscle fibers. The muscle stimulation decreases as fatigue sets in. The source of this fatigue has been speculated to be reduced concentrations of ATP and ADP, or simply put, our energy source. This decrease in energy reduces our action potential, and lowers the function of the sarcoplasmic reticulum or sarcolemma. More evidence has suggested that an imbalance in the Na/K+ channel pump (sodium/potassium) is the likely intramuscular culprit leading to fatigue (2). It has been shown that an increased presence of K+ in the interstitial space limits the membrane excitability potential (2).
Chronic disease has proven to increase the rate of intramuscular fatigue. For type II diabetics, exercise is further complicated by an impaired ability to deliver oxygen, and metabolic substrates to the working muscle, as well as a decreased vascular function in removing byproducts (1). Moreover, diabetics fatigued at a higher rate, and produce 50% less angular impulse than healthy people. These incidences could be explained by reports confirming that Na/K pump dysfunction, observed in diabetics, causes neuronal hyperexcitability (1).
As for healthy people, intramuscular fatigue during exercise has been attributed to increases in potassium following 30 minutes of intense exercise training (3). If potassium rises to concentration between10–12.5 mmol, a reduction of 40 - 100% in maximum twitch or tetanic force can occur (3). In Green et. al. (2000) study the resting potassium concentration was 4.4 mmol, and increased 11 mmol following the 60 minutes plantar flexion exercise protocol. This increase was correlated as being a positive marker for exercise intensity.
Many people diagnosed with type II diabetes wonder what is an excellent exercise time frame to commit to. Consistency is the key to their success. With that being said, 30 minutes of moderate intensity exercise is a realistic goal for many type II diabetics. Keep in mind that 30 minutes is an excellent marker, however, a deconditioned type II diabetic might begin to fatigue within 10 to fifteen minutes of beginning their exercise routine. Therefore, the deconditioned population of type II diabetics would benefit from breaking up their daily workouts into two to three daily sessions of 15 minutes to 10 minutes, respectively.
References
1. Allen, M. D., Kimpinski, K., Doherty, T. J., & Rice, C. L. (2015). Decreased muscle endurance associated with diabetic neuropathy may be attributed partially to neuromuscular transmission failure. Journal of applied physiology (Bethesda, Md. : 1985), 118(8), 1014–1022. https://doi.org/10.1152/japplphysiol.00441.2014
2. Gardiner, P. F. (2011). Advanced neuromuscular exercise physiology. Leeds, Illinois: Human Kinetics.
3. Garland, S. J., & Gossen, E. R. (2002). The muscular wisdom hypothesis in human muscle fatigue. Exercise and sport sciences reviews, 30(1), 45–49. https://doi.org/10.1097/00003677-200201000-00009