By Brandon Roberts

It’s the end of the year and while writing your goals for 2018, you jot down one based on exercise. It might be to start going to the gym more regularly or to start a new fitness program. What exactly happens in those first few months? We know exercise is good for us, but how? Well, in this article we’ll dive into the physiological adaptations that occur due to resistance training, as well as some of the psychological changes that occur.

You walk into the gym and hit the weights. Over the first few weeks you’re feeling great, increasing the weight each week as you feel more confident with every exercise. However, these newfound strength gains occur at a far greater rate than actual muscle growth (Figure 1). Side effects of the increased strength include improved ability to pour a gallon of milk or open a jar of jam. These initial strength increases are mostly neural, meaning the nervous system is adapting to new skills, which is part of the motor learning process (Sale, 1988, Moritani & deVries, 1979). You may also encounter muscle discomfort along the way, which is known as delayed onset muscle soreness (DOMS). DOMS isn’t an indicator of a successful workout or of lactic acid build-up in the muscle, but rather a combination of muscle damage, cell swelling, and activation of pain receptors.

During the next few weeks, you will see an increase in muscle size, but it will be a very slow process. Most of the increase is due to elevated levels of glycogen within the muscle. Most studies find anywhere from a 3 to 10% increase in muscle size after 4-8 weeks of training (Goreham et al., 1999, Defreitas et al., 2011). This is usually enough for people to feel the difference and you may even begin to see it in the mirror.

We know muscle and bone are strongly linked both anatomically and functionally. We can’t move very well without both.  Thus, resistance training also helps create new bone (osteogenic effect). There is a strong correlation with training and bone mineral composition (Grahned et al., 1987). Although the changes in bone are even slower than muscle, with only a 0.25%-0.5% increase in the first several months of training (Kelley et al., 2013). This increase in bone mineral density can help prevent fractures and is very important for long term health.

An adaptation that people often forget when starting a training program are the psychological benefits. This all starts with creating a habit of exercise, which can take a while. The literature suggests it takes 60-80 days to reach automaticity with an exercise habit (Lally et al., 2009). Once you’ve created the habit of exercise, even if you miss a workout here or there, it will be easier to continue.

Another benefit to resistance training is increased mental well-being.  Resistance training is associated with reductions in anxiety, improvements in cognition, and improvements in self-esteem (O’Connor, 2010).  While most of the research is in the elderly or those with cognitive impairment, there is a significant amount of data to support the enhancement of cognition with exercise.

Exercise is all about creating stress and adapting. I didn’t cover endurance exercise in this article, but it also has a plethora of benefits – some similar and some different. For a broader look at the benefits of strength training, see Figure 2. After all my time in academia and personal training, I’ve found that almost everyone can benefit from some type of exercise.


Sale, D. G. (1988). Neural adaptation to resistance training. Medicine and Science in Sports and Exercise, 20(Suppl.), S135-S145.

Moritani, T., & deVries, H. A. (1979). Neural factors versus hypertrophy in the time course of muscle strength gain. American Journal of Physiological Medicine, 58, 115-130.

Goreham, C., Green, H.J., Ball-Burnett, M., & Ranney, D. (1999). High-resistance training and muscle metabolism during prolonged exercise. American Journal of Physiology, 276(3 Pt 1), E489-96.

Defreitas, J.M., Beck, T.W., Stock, M.S., Dillon, M.A., & Kasishke, P.R. (2011). An examination of the time course of training-induced skeletal muscle hypertrophy. European Journal of Applied Physiology, 111(11),2785-2790.

Granhed, H., Jonson, R., & Hansson, T. (1987). The loads on the lumbar spine during extreme weight lifting. Spine, 12(2),146-149.

Kelley, G.A., Kelley, K.S., & Kohrt, W.M. (2013). Exercise and bone mineral density in premenopausal women: a meta-analysis of randomized controlled trials. International Journal of Endocrinology, 2013, 741639.

Lally, P., Wardle, J., & Gardner, B. (2011). Experiences of habit formation: A qualitative study. Psychology, Health & Medicine, 16(4), 484-489.

Brandon RobertsBrandon Roberts is a strength & physique coach, scientist, and fitness writer. He works with The Strength Guys to help athletes perform better using an evidence-based approach. He contributes to numerous fitness websites while also publishing in peer-reviewed academic journals.