In a recent paper published in The Journal of Physiology, researchers compared the impacts of morning and afternoon aerobic exercise for people with metabolic syndrome [1].
Hitting the gym after breakfast or after lunch
Metabolic syndrome (MetS) has been defined as a group of “cardiometabolic risk factors and comorbidities.” People with metabolic syndrome are at a higher risk of cardiovascular disease and type 2 diabetes [2]. Exercise can be used as a cost-effective strategy to delay the progression of MetS.
However, since there are multiple methods for approaching exercise, researchers have been searching for the ones with the strongest and clearest effects, including in timing. There is still no consensus as to what timing brings the best results. Some researchers have argued for morning exercise [3-5], others have supported evening exercise [6-8], and still others have claimed that the time of day doesn’t matter [9].
Earlier is better
This study followed a group of 139 volunteers that had metabolic syndrome and a BMI of 30.6 and who were physically inactive before the study. The participants took part in a 16-week-long supervised high-intensity aerobic exercise program. They exercised three times per week on stationary bikes. One group exercised in the morning (AMEX), and the second exercised in the afternoon (PMEX).
A dietitian also consulted participants on their dietary needs. The advised macronutrient distribution range consisted of carbohydrates (45-65% of energy), protein (10-35% of energy), and fat (20-35% of energy). Saturated and trans fats were to be avoided.
Study participants were asked for a monthly 3-day nutritional intake diary. Researchers also tracked the participants’ activity levels, specifically steps per day, and standing and supine time. To measure activity, for 48 hours every month, volunteers wore wristband activity monitors. This program prevented major differences of calorie intake and physical activity levels between the participant groups.
After 16 weeks of training, both groups that exercised had decreased body weight. However, the changes were rather small: 0.8 kilogramsfor AMEX and 1 kilogram for PMEX.
Additionally, researchers observed improvements in metabolic factors in both exercise groups, and there were no significant differences between them. The researchers observed a significant reduction in waist circumference, reduction in fat mass, diastolic blood pressure, and the endurance and oxygen consumption metric VO2max.
However, there were differences between the two groups. The AMEX group had higher improvements in systolic blood pressure, plasma fasting insulin concentration, and insulin resistance.
To combine metabolic syndrome components into one metric, the researchers used the MetS Z score. This includes serum levels of cholesterol, triglycerides, glucose, waist circumference, systolic blood pressure, and diastolic blood pressure. A lower score represents better metabolic health.
The researchers observed improvements in MetS Z scores in both exercise groups compared to controls, where such scores had no improvements after 16 weeks. The AMEX group had greater improvements in MetS Z scores than the PMEX group.
Strengths and limitations
As with every study, this one has its strong and weak points. While this was a randomized controlled trial with a large sample size with analyzed physical activity and supervised training sessions, the particpants’ individual preferences for exercise were not part of this study. The authors didn’t employ 24-hour ambulatory blood pressure measurements, which may have provided more robust information about circadian blood pressure patterns. Additionally, the authors limited the research to aerobic exercise and didn’t investigate strength training.
In summary, our data suggest that high-intensity aerobic exercise training for 16 weeks in the morning (AMEX) is more efficient at reducing insulin sensitivity [i.e. insulin concentration and insulin resistance (HOMA-IR)] and systolic blood pressure than similar training in the afternoon (PMEX) in individuals with MetS.
Literature
[1] Morales-Palomo, F., Moreno-Cabañas, A., Alvarez-Jimenez, L., Mora-Gonzalez, D., Ortega, J. F., & Mora-Rodriguez, R. (2023). Efficacy of morning versus afternoon aerobic exercise training on reducing metabolic syndrome components: A randomized controlled trial. The Journal of physiology, 10.1113/JP285366. Advance online publication.
[2] Alberti, K. G., Eckel, R. H., Grundy, S. M., Zimmet, P. Z., Cleeman, J. I., Donato, K. A., Fruchart, J. C., James, W. P., Loria, C. M., Smith, S. C., Jr, International Diabetes Federation Task Force on Epidemiology and Prevention, Hational Heart, Lung, and Blood Institute, American Heart Association, World Heart Federation, International Atherosclerosis Society, & International Association for the Study of Obesity (2009). Harmonizing the metabolic syndrome: a joint interim statement of the International Diabetes Federation Task Force on Epidemiology and Prevention; National Heart, Lung, and Blood Institute; American Heart Association; World Heart Federation; International Atherosclerosis Society; and International Association for the Study of Obesity. Circulation, 120(16), 1640–1645.
[3] Alizadeh, Z., Younespour, S., Rajabian Tabesh, M., & Haghravan, S. (2017). Comparison between the effect of 6 weeks of morning or evening aerobic exercise on appetite and anthropometric indices: a randomized controlled trial. Clinical obesity, 7(3), 157–165.
[4] Chomistek, A. K., Shiroma, E. J., & Lee, I. M. (2016). The Relationship Between Time of Day of Physical Activity and Obesity in Older Women. Journal of physical activity & health, 13(4), 416–418.
[5] Schumacher, L. M., Thomas, J. G., Raynor, H. A., Rhodes, R. E., & Bond, D. S. (2020). Consistent Morning Exercise May Be Beneficial for Individuals With Obesity. Exercise and sport sciences reviews, 48(4), 201–208.
[6] Savikj, M., Gabriel, B. M., Alm, P. S., Smith, J., Caidahl, K., Björnholm, M., Fritz, T., Krook, A., Zierath, J. R., & Wallberg-Henriksson, H. (2019). Afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes: a randomised crossover trial. Diabetologia, 62(2), 233–237.
[7] van der Velde, J. H. P. M., Boone, S. C., Winters-van Eekelen, E., Hesselink, M. K. C., Schrauwen-Hinderling, V. B., Schrauwen, P., Lamb, H. J., Rosendaal, F. R., & de Mutsert, R. (2023). Timing of physical activity in relation to liver fat content and insulin resistance. Diabetologia, 66(3), 461–471.
[8] Di Blasio, A., Di Donato, F., Mastrodicasa, M., Fabrizio, N., Di Renzo, D., Napolitano, G., Petrella, V., Gallina, S., & Ripari, P. (2010). Effects of the time of day of walking on dietary behaviour, body composition and aerobic fitness in post-menopausal women. The Journal of sports medicine and physical fitness, 50(2), 196–201.
[9] Janssen, I., Campbell, J. E., Zahran, S., Saunders, T. J., Tomasone, J. R., & Chaput, J. P. (2022). Timing of physical activity within the 24-hour day and its influence on health: a systematic review. Moment choisi pour faire de l’activité physique sur 24 heures et son influence sur la santé : revue systématique. Health promotion and chronic disease prevention in Canada : research, policy and practice, 42(4), 129–138.
