Human beings possess an internal time management mechanism (circadian central clock) that coordinates dark and light activities, while managing such activities as, skeletal muscle preservation, liver health, and fat tissue (peripheral clock), that occur during fasting (especially night-time), activity, and the recovery-repair process that occurs during sleep.
As we age or when we succumb to certain conditions and disease processes, like insulin resistance and type 2 diabetes, homeostasis (balance) in our clock mechanisms can be negatively affected, without intervention.
Such interventions can involve exercise – the timing of which may normalize or stabilize a dysfunctional human clock mechanism. This anomaly is especially true for night shift workers, even those without metabolic challenges.
According to "Exercise Training Elicits Superior Metabolic Effects, When Performed in the Afternoon Compared to Morning in Metabolically Compromised Humans," which appeared in December of 2020 in Physiological Reports, “exercise training is the first-line strategy to counteract skeletal muscle insulin resistance and ameliorate elevated plasma glucose levels.”
The study authors, from the Netherlands, comment that, “the recent insights into the role of the circadian clock in the etiology of T2DM (type 2 diabetes) have raised the suggestion that the timing of exercise may affect the training-mediated effects on glucose homeostasis.”
The researcher report that, “consecutive bouts of high-intensity interval exercise during two weeks, acutely induce more beneficial 24-hour glycemic profiles in T2DM subjects, when performed in the afternoon, as compared to a morning training regime.”
To investigate whether the timing of exercise affected long-term metabolic health training adaptations in metabolically compromised individuals, the investigators analyzed data from a study assessing the effect of exercise training on a large range of metabolic health outcomes.
The study group, which included thirty-two adult males (58 ± 7 years), with a body mass index greater than 26 (overweight) at risk for or diagnosed with type 2 diabetes, performed twelve weeks of supervised exercise.
Twelve volunteers exercised in the morning from 8.00–10.00 a.m., while twenty individuals exercised in the afternoon from 3.00–6.00 p.m.
The exercise sessions consisted of twice weekly stationary cycling for 30 minutes at 70% of a pre-determined workload, and one day of resistance exercise, using three sets of ten repetitions at 60% of maximum voluntary contractions in large muscle groups (leg extension, leg press, chest press, lat. pulldown, triceps and biceps curls).
Pre-participation laboratory and physiological assessment, with appropriate exclusion criteria was performed – leading to the conclusion that, “compared to participants who trained in the morning, participants who trained in the afternoon experienced superior beneficial effects of exercise training on insulin-stimulated peripheral glucose disposal, insulin-mediated suppression of adipose tissue lipolysis, fasting plasma glucose levels, exercise performance, and fat mass.”
In addition, “exercise training in the afternoon also tended to elicit superior effects on basal hepatic glucose output.”
The researchers concluded that, “the timing of an exercise training session is a crucial environmental cue, when aiming to improve glucose homeostasis in metabolically compromised subjects, and elucidates that performing afternoon exercise training might be more optimal than exercising at morning hours.”