Does It Matter If You lift in the Morning or the Evening?
Six weeks of strength training improved muscle and metabolic health equally in both groups, but was morning or evening better?
A new randomised controlled trial says no. Researchers from the University of Glasgow put healthy adults through six weeks of training at either 6–10 am or 4–8 pm and measured muscle size, muscle strength, and insulin sensitivity before and after. Both groups improved, but neither group improved more than the other. The verdict: train when you can.
What They Studied
The debate around exercise timing has been fuelled by the idea that the body’s internal clock, circadian rhythms, might make certain times of day better for building muscle or improving metabolic health. Evening exercise has long been theorised to have an edge for insulin sensitivity, and strength has been known to peak in the late afternoon. This trial was designed to test those theories in healthy adults without diabetes.
How It Was Done
Thirty-six healthy adults, averaging 30 years old and a BMI of around 28 kg/m², were split into three groups: morning training, evening training, and a control group that did nothing structured. Both training groups performed the same eight-exercise resistance training program three times per week for six weeks, working at 80% of their one-rep max to failure each set. The program included bench press, bicep curl, lat pulldown, overhead press, lateral raise, leg extension, leg curl, and calf raise. Attendance was 100% across both groups.
Muscle size was measured using ultrasound on the vastus lateralis (the outer quad muscle). Strength was assessed via knee extensor torque and one-rep max. Insulin sensitivity was tested using an oral glucose tolerance test. Participants also wore continuous glucose monitors for several weeks to track real-world blood sugar responses.