Author(s): DIGHRIRI, A., LITHGOW, H., LOGAN, G., GABRIEL, B., DUNNING, E., JOHNSTON, L., BOYLE, J., GRAY, S., Institution: UNIVERSITY OF GLASGOW, Country: UNITED KINGDOM, Abstract-ID: 1854

INTRODUCTION:
There are many health benefits associated with resistance exercise, including stimulation of glucose metabolism, improved cardiovascular fitness and enhanced muscular strength. However, it is still unclear when is the best time to perform resistance exercise. We conducted a randomised controlled trial to examine the impact of time of day on muscle and metabolic responses to resistance exercise in healthy adults.

METHODS:
We recruited 36 participants, inclusion criteria age between 18-45 years old with body mass index (BMI) >23.0kg/m². Exclusion criteria included having undergone surgery for weight loss, had prior history of heart, lung, cancer, kidney, endocrine, or liver disease. Participants were randomised into either a control, exercise in the morning (6:00-10am) or exercise in the evening (4:00-8:00pm) group. Those in the exercise groups performed 8 resistance exercises (1 set to failure) 3 times a week for 6 weeks, at their allocated time of day. At baseline and during the last visit, we measured insulin sensitivity during an oral glucose tolerance test along with measurements of grip strength, vastus lateralis muscle thickness and knee extensor maximal torque.

RESULTS:
We randomly assigned participants to three groups: morning exercise (n= 12); evening exercise (n= 11); or control group (n= 13). Two way repeated measured ANOVA showed effects of time for maximal torque (p<0.001), insulin sensitivity (p=0.015) and muscle thickness (p=0.008) but not grip strength (p=0.633). No group or interaction effects were observed. In the morning group there were increases in maximal torque (+5.54 (1.87 to 9.21) Nm p=0.007) and insulin sensitivity (+15.39 (2.93 to 27.85) mg l2 mmol−1 mU−1 min−1 p=0.020) with no increases in muscle thickness (+1.17 (-0.02 to 2.25) mm p =0.054). In the evening group there were increases in muscle torque (+5.68 (2.36 to 8.99) Nm p=0.003) and muscle thickness (+1.20 (0.37 to 1.97) mm p=0.009), with no increases in insulin sensitivity (+10.68 (-7.77 to 29.13) mg l2 mmol−1 mU−1 min−1 p=0.223). No increases in any variable in the control group were seen.
CONCLUSION:
The results of the present study indicate, although sample size was limited, that resistance exercise increases muscle strength, muscle size and insulin sensitivity with very little difference in magnitude of effect between performing exercise in the morning versus the evening.