Training for health: be an owl, not a lark

SPB looks at more new research suggesting that late afternoon/evening training is better for athlete health

It was only last month that SPB published new research on how the timing of training influences the performance outcomes gained. In short, what that research showed was that when participating in a rounded training program consisting of resistance training, interval-type sprint exercise, stretching and steady-state endurance exercise, men and women reacted differently at different times of the day⁽¹⁾. In a nutshell, men training in the late afternoon/early evening experienced a significantly greater reduction in blood pressure, increased fat oxidation and significantly less fatigue compared to the same exercise program performed in the morning. Women meanwhile experienced greater fat loss and gained greater lower body strength when they morning trained, but gained more upper body strength and power when they evening trained.

Exercise, blood chemistry and cardiovascular health

Hot on the heels of that study comes a new piece of research conducted by researchers at Waseda and Yokohama Universities in Japan, and which has just been published the journal ‘Frontiers in Endocrinology’. In this study, the researchers investigated the effects of one hour of low to moderate-intensity endurance exercise (treadmill walking) on the subsequent levels of blood glucose and blood fats (lipids) over the next 24 hours in healthy, fit men⁽²⁾.

Why the focus on blood glucose and triglyceride levels? Well, hyperlipidemia (excess blood fats) and hyperglycemia (excess blood glucose) are known to be very significant risk factors for cardiovascular disease (CVD), the world’s biggest killer^(3,4). Controlling these factors therefore is important for heart health.

The good news is that endurance exercise has a positive/healthy effect on many established CVD-related risk factors, including hyperlipidemia and hyperglycemia^(5,6). However, the body’s ability to control and regulate blood glucose and lipids is known to vary throughout the day as a result of the daily or ‘circadian’ rhythm⁽⁷⁾. These differences are not trivial; previous studies have demonstrated that morning/evening variations in glucose tolerance are so great that adults with apparently normal glucose tolerance in the morning are metabolically equivalent to pre-diabetics in the evening⁽⁸⁾! In addition, post-meal blood lipid (triglyceride) concentrations have been shown to be higher in the evening than in the morning, due to circadian variations in lipid tolerance⁽⁹⁾.

Unanswered question

If endurance exercise favorably affects the regulation of blood glucose and lipids, which are themselves affected by the night/day circadian rhythm, a natural question to ask is ‘does altering the time of day that exercise is undertaken affect the blood glucose/lipid health benefits it delivers’? Since there’s very little data on this topic, the Japanese researchers mentioned above decided to try and provide some definitive answers.

Twelve healthy, fit young men participated in a randomized crossover trial. The participants were assigned to morning (09:00-11:00) or late afternoon (16:00-18:00) endurance exercise sessions for a week, consisting of supervised exercise sessions on Mondays, Wednesdays, and Fridays. In the morning and evening trials, the participants walked for 60 minutes on a treadmill at 60% of their maximal oxygen uptake (low to moderate intensity), achieved by altering treadmill speed. Following a 2-week ‘wash-out’ period, the participants performed the exercise training regimen at the other time point – ie those who had exercised previously between 09.00-11.00 now exercised at 16.00-18.00 and vice versa. Continuous glucose monitoring was used to evaluate blood glucose fluctuations during each 24-hour trial period, and blood samples were collected before and after each intervention to examine blood lipid and hormonal responses.

The findings

In short, afternoon exercise produced very significantly greater benefits than the same training performed in the morning. The ‘area under the curve’ (AUC – a measure of the total quantity) of the glucose level changes for the 24-hour period after the late afternoon intervention revealed significantly lower values compared to exercising in the morning (see figure 1). Moreover, The AUC of glucose level changes after each meal was also lower following late afternoon training versus morning training, especially for breakfast and dinner. In plain English, when the men trained in the afternoon, their levels of blood glucose were lower throughout the day compared to when they trained in the morning (a good thing for cardiovascular health), and they suffered lower peaks in blood glucose after breakfast and lunch (also a good thing).

Afternoon training also produced greater benefits than morning training in terms of blood lipids. When the men trained in the afternoon, they experienced a significant decrease in blood triglycerides and in the ratio of triglycerides to HDL cholesterol. A lower ratio of triglycerides to HDL is a GOOD thing as it means relatively more HDL cholesterol (the healthy sort) is available to transport excess lipids to the liver for destruction – again, beneficial for hearth health.

Figure 1: Blood glucose levels following morning vs. afternoon training⁽²⁾

Concentrations of blood glucose in the four hours following a meal, with breakfast (A), lunch (B), and dinner (C), and the blue and red lines indicate the morning and late afternoon trials.

Implications for athletes

Although they are aware of the health benefits of exercise, reducing the risk of cardiovascular disease is something that barely registers for many athletes, especially those who are younger. However, not all athletes are young, and despite the protective effects of exercise, metabolic disorders affecting blood glucose and lipid regulation can and do exist - even among athletes who train hard and train regularly. Indeed, contrary to popular belief, the soaring incidence of diabetes is not only confined to the elderly or obese; athletes can and do suffer from late onset type II diabetes and the chances are that some of you reading this may even go on to develop the condition in years to come – see this article. In addition, many older athletes are primarily motivated to take up competitive sport because of a desire to maintain or regain heart health.

The good news is that for those men who do want to gain the maximum heart health benefits of exercise, simply swapping out your morning exercise session for the same session performed in the late afternoon/early evening will give you very significantly increased benefits. Why does this effect occur? One theory is that late afternoon endurance exercise can favorably affect blood glucose fluctuations by interacting with other key hormones in the body involved in blood glucose regulation, and which are secreted in different amounts at different times of the day. However, we don’t know for sure.

So far we haven’t mentioned women and the question is can women get the same blood health benefits by switching from morning to late afternoon sessions? The answer again is that we don’t really know. Previous research found that men can have up to twice as high post-meal blood triglyceride concentrations and much greater morning/evening variations compared to women⁽¹⁰⁾. These sex-based differences are thought to be due to the effects of the female hormone estrogen on lipid metabolism⁽¹¹⁾. This might help explain why men are more likely to succumb to cardiovascular disease than women⁽¹²⁾. Also, we know that in diabetes (a disorder of blood glucose control) the hormone testosterone that reduces the risk of diabetes in men actually increases the risk in women⁽¹³⁾. What this means is that when it comes to blood glucose and lipids, the control mechanisms are not exactly same, which is why more research will be needed. Girls – as soon as we have any data, we will be sure to let you know!

References

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