Does strength training help against insulin resistance?

Strength training increases the density of a protein in muscles that helps transport sugar into the cell (glucose transporter type 4). Having more of this protein means that muscles respond better to insulin. At the same time, the average blood sugar level over three months (measured as HbA1c) falls and visceral fat around the organs decreases. Multiple studies point to this effect, although the evidence is consistently rated as moderate in strength.

The greatest gains have been documented in people who combine strength and endurance training. An analysis of 20 studies involving more than 1,200 people with type 2 diabetes and excess weight showed that such a combined programme leads to lower blood sugar levels, better blood pressure, fewer inflammatory markers in the blood, and a higher quality of life compared with standard care. The researchers themselves describe the quality of the evidence as moderate and call for more robust follow-up research.

Strength training as a standalone intervention is less convincing when looking at cardiovascular risk factors in people with metabolic syndrome who do not yet have diabetes. A systematic review found no statistically significant effect for that group, but attributes this partly to a lack of available studies. It is therefore too early to say that it does not work in that group; it simply has not been studied enough yet.

Exercise in general, including strength training, improves the insulin sensitivity of muscles independently of weight loss. Some effects even occur without insulin needing to play any role. Weight loss itself provides additional benefit on top of that, but it is best achieved by combining strength training with changes in eating and lifestyle habits, rather than through exercise alone.