Latest News & Research: 30 April 2019

This week: How to stop resistance training damaging endurance training • Exercise timing and body response • How the body adapts to occasional overeating


How to stop resistance training damaging endurance training

James Cook University scientists say they have the solution for a problem exercisers experience when they combine endurance and weight training.

Dr Kenji Doma led the review paper. He said his own work and that of other scientists had previously discovered that resistance training, such as weight lifting, may harm performance in endurance training, such as running, when the two are combined on the same or separate days (commonly known as ‘concurrent training’).

‘Based on previous evidence, we suspect that if appropriate recovery is not accounted for between each training mode, it may impair endurance development’ he said.

Dr Doma said the physiological stress caused by a typical resistance training bout of 40 to 60 minutes can continue for several days post-exercise, as opposed to a full recovery within 24 hours following a typical endurance training bout.

‘We wanted to increase the awareness of resistance training-induced fatigue in the hope of encouraging coaches to think about aspects such as the order of the training, the recovery period, training intensity, etc. With this new work, we think we now have a roadmap for them to follow’ said Doma.

He said the team think there are several training variables that may influence the way in which resistance training impacts the quality of endurance training.

They include the intensity of resistance and endurance training sessions, the volume of resistance training, the speed in which resistance training is performed, the recovery period between resistance and endurance training, and the order of resistance and endurance training sessions.

‘By understanding the influence these variables have, it means that both resistance and endurance  training can be prescribed in such a way that minimises fatigue between modes of training, which could optimise the quality of endurance training sessions’ said Doma.

Doma said it was important that fatigue be monitored between the different training types and different periods of rest enforced after different levels of either endurance or resistance training.

‘One of the easiest recommendations to follow is that if the performance of resistance and  endurance training sessions on the same day is unavoidable, endurance training sessions should be done prior to resistance training irrespective of the intensity of either, with at least half a day of recovery in-between training sessions’ he said.

Doma said the findings were made freely available in the published paper with the hope that coaches and both amateur and professional endurance athletes undertaking concurrent training could use them to increase performance.

Source: James Cook University


Exercise timing and body response

Two recent papers in the journal Cell Metabolism confirm that the circadian clock is an important factor in how the body responds to physical exertion. The studies focused on different components of exercise, thereby complementing each other. Based on this work alone, it's too early to say when the best time is for you to go for a jog. But at least in the lab, exercise in the evening seems to be more productive, although human lifestyles are much more complicated and so this area of research is only just beginning.

‘It's quite well known that almost every aspect of our physiology and metabolism is dictated by the circadian clock’ said Gad Asher of the Department of Biomolecular Sciences at the Weizmann Institute of Science, who is senior author of one of the studies; ‘This is true not only in humans but in every organism that is sensitive to light. We decided to ask whether there is a connection between the time of day and exercise performance.’

‘Circadian rhythms dominate everything we do’ added Paolo Sassone-Corsi of the Center for Epigenetics and Metabolism at the University of California, Irvine, who is senior author of the other paper; ‘Previous studies from our lab have suggested that at least 50% of our metabolism is circadian, and 50% of the metabolites in our body oscillate based on the circadian cycle. It makes sense that exercise would be one of the things that's impacted.’

Both research teams looked at the association between time of day and exercise performance primarily in mice. Because mice are nocturnal, one thing they had to do was translate mouse timing to human timing, by distinguishing between the active phase and resting phase of the mice rather than using numbers on the clock.

Asher's group started by putting mice in treadmills at different times of day within their active phase. They examined the exercise capacity of mice upon different exercise intensities and regimens and found that overall exercise performance is substantially better (about 50% on average and more in some protocols) in the ‘mouse evening’ (toward the end of their active time) compared to the morning hours. These daily differences were diminished in mice that had mutant clocks -- supporting a potential role of the clock in the observed variance in exercise performance.

To identify a potential determinant of daily variance in exercise performance, they applied high-throughput transcriptomics and metabolomics on muscle tissue. The researchers found that in response to exercise in the ‘mouse evening’ there were higher levels of a metabolite called ZMP (5-aminoimidazole-4-carboxamide ribonucleotide). ZMP is known to activate metabolic pathways that are related to glycolysis and fatty acid oxidation through activation of AMPK, which is a master cellular metabolic regulator. Therefore, it is likely to contribute to the increased exercise capacity in the evening. ‘Interestingly, ZMP is an endogenous analog of AICAR [aminoimidazole carboxamide riboside], a compound that some athletes use for doping’ Asher says.

The researchers also studied 12 humans and found similar effects. Overall, the people in the study had lower oxygen consumption while exercising in the evening compared with the morning; this translated to better exercise efficiency.

Sassone-Corsi's team also put mice on treadmills, but they had a different approach. Using high-throughput transcriptomics and metabolomics to look at a wide range of possible factors, they characterised the changes in the mice's muscle tissue that occur in response to exercise. This allowed them to look at processes like glycolysis (which contributes to sugar metabolism and energy production) and lipid oxidation (fat burning).

They found that a protein called hypoxia-inducible factor 1-alpha (HIF-1) plays an important role and that it is activated by exercise in different ways depending on the time of day. HIF-1 is a transcription factor that is known to stimulate certain genes based on oxygen levels in tissue. ‘It makes sense that HIF-1 would be important here, but until now we didn't know that its levels fluctuate based on the time of day’ Sassone-Corsi said; ‘This is a new finding.’

Based on the work from the UC Irvine team, exercise seemed to have the most beneficial impact on the metabolism at the beginning of the active phase phase (equivalent to late morning in humans) compared with the resting phase (evening).

The researchers note that even though circadian clocks have been conserved throughout evolution, translating the findings to humans is not so straightforward. One reason is that humans have more variation in their chronotypes than mice living in a lab; ‘You may be a morning person, or you may be a night person, and those things have to be taken into account’ Sassone-Corsi says.

Source: Science Daily


How the body adapts to occasional overeating

Overeating has been found to impair blood sugar (glucose) control and insulin levels. A new Australian study suggests that the duration of a bout of overeating can affect how the body adapts glucose and insulin processing when calorie intake increases.

Understanding how overeating causes changes in blood sugar control and insulin processing may help scientists learn more about metabolic disease.

Researchers from Deakin University studied a small group of healthy, lean men with an average age of 22. Volunteers participated in a short-term trial consisting of five days ‘indicative of humans overeating during festivals and holidays’ and a long-term model of chronic overeating lasting 28 days. The nutritional composition of the volunteers’ diet was representative of a typical Australian diet (55% carbohydrates, 35% fat and 15% protein). The ‘overfeeding’ portion of the diet included high-calorie snacks such as chocolate, meal replacement drinks and potato chips to add approximately 1,000 more calories to the men’s normal food consumption each day. The research team measured the volunteers’ weight, fat mass, blood sugar and insulin levels before the trial began and again after five and 28 days.

Although the amount of visceral fat that surrounds internal organs increased substantially, short-term overeating did not have a significant effect on the men’s weight or fat mass. In addition, fasting levels of blood sugar and C-peptide – an amino acid the body releases in response to increased production of insulin – did not change. This finding was surprising because fasting levels of endogenous glucose – new glucose the body produces in addition to what it has already stored for future use – increased during the short-term trial.

Chronic overeating increased the amount of total body fat and visceral fat as well as post-meal blood sugar and C-peptide levels. However, it did not alter fasting blood sugar levels, endogenous glucose production or the rate of glucose removal from the body (glucose disposal). This may be because the nutrient profile in the long-term trial was consistent with a typical diet and dietary fat percentages did not increase. Long-term overindulgence in fatty foods, instead of more nutritionally balanced foods, may be an important factor that causes rapid changes in blood sugar control.

These findings ‘suggest that early adaptations in response to carbohydrate overfeeding are directed at increasing glucose disposal in order to maintain whole-body insulin sensitivity’ the researchers wrote.

Source: American Physiological Society