Exploded view of the human skeletal muscle structure.
W
hen you start a resistance training or weightlifting routine, there are many physiological effects - some of which start to take place right after your first workout. These metabolic, hormonal and structural changes are all your body’s way of adapting to the “stress” of lifting weights. The following is a summary of what happens physiologically after 48 hours, 4 weeks, 8 weeks and 12 weeks of resistance training.
Changes during/within 48 hrs post prolonged, resistance training
A single bout of resistance training can lower blood sugar to hypoglycemic levels in normal, healthy individuals. For diabetics this naturally occurring mechanism is especially beneficial in acting towards down regulation of blood glucose, as this effect can last up to several days. Improved glucose removal and metabolism may last for several hours and possibly up to a couple days after an exercise session. Later on during an exercise bout, as glucose levels become depleted, the glycogenolysis/gluconeogenesis-stimulating hormone glucagon is released to regulate the low blood sugar levels.
Since resistance training mainly involves anaerobic energy metabolism, which utilizes glucose as a substrate to produce ATP, longer resistance bouts result in more depletion of blood glucose. This is the reason why resistance training is recommended over cardiovascular training for the diabetic population. The acute effects of resistance training involved during a single session include increasing the exercising muscles’ insulin sensitivity, which can lead to long-term control of blood sugar if done regularly, week after week. With increased insulin sensitivity of muscle tissue, insulin uptake by peripheral cell receptors occurs efficiently and requiring less insulin to be released. As a result of this, more blood glucose will be converted to glycogen for storage in the muscle instead of being converted to triacylglycerol for storage in adipose tissue.
Testosterone levels remain increased and cortisol levels decreased for up to 48 hours post exercise. There will be no body composition or major neuromuscular adaptations at this point in time. Osteoblast activity will be stimulated as a result of the strain produced from resistance training and will start working towards increasing calcium deposition in bone within the 48 hours after training.
Changes after 4 weeks of continuous resistance training
After 4 weeks there won’t be much of a change in body composition. Taking into account the caloric expenditure of exercise and assuming a low-fat diet including high-glycemic index carbohydrates is followed, there will be a slight decrease in fat mass. There will be no noticeable increase in muscle mass. Mostly all the strength gains at this point will be due to neuromuscular adaptations. Bone density will have increased due to the effects of increased testosterone and increased osteogenic activity.
Changes after 8 weeks of continuous resistance training
After 8 weeks there will more a more apparent decrease in body fat and increase in muscle mass. The increased levels of testosterone and growth hormone have had sufficient time to elicit changes favoring increased muscle fiber size and decreased fat cell size. Along with increased bone mineral density, an increase in bone mass will start to become significant.
Changes after 12 weeks of continuous resistance training
The increased muscle mass obtained after 12 weeks of continuous resistance training will provide more receptor sites for insulin uptake, further increasing insulin sensitivity. Assuming a major decrease in fat mass, in part due to increased basal or resting metabolic rate (BMR/RMR) from the added muscle, insulin sensitivity would increase even more due to the smaller-sized fat cells eliciting a lesser insulin resistant effect compared to when they were larger (more dense). A significant increase in bone mass will have accumulated compared to pre-training. The increased resting levels of testosterone will act towards preventing osteoporosis.
Diabetes and Resistance Training
It is imperative that diabetics continue to exercise and eat healthy to maintain glycemic control. Resuming sedentarism even for only a couple weeks can result in poor regulation of blood glucose, especially in those that are still overweight/obese and/or whose cause of diabetes is genetic. Just as the ill effects (glucose intolerance) of diabetes can be reversed through exercise, they can just as quickly return with a sedentary lifestyle. Type 2 diabetics can possibly be cleared of the disease if a healthy, fit lifestyle is maintained for a long enough period.
Osteoporosis and Resistance Training
Just as the positive effects of resistance training on glycemic control can reverse once it is stopped, the osteogenic effects of strength training are also reversible. Load-bearing exercise is recommended for those at risk or suffering from this condition. The osteoporotic effects of sedentarism and poor diet can be successfully reversed, though a physician-approved resistance training regimen should be taken up immediately upon signs of osteoporosis. Sufficient intake of vitamin D and calcium either through diet or supplement should also be ensured prevent osteoporosis.
