Strength training: why gyms are always full on Mondays

On Mondays, all hell breaks loose in gyms. At the population level, there’s nothing wrong with this – quite the opposite, in fact. For some gym-goers however, this crowd-induced stress proves problematic. After all, who wants to have to constantly wait around until «their» machine is finally free?

The health benefits of doing exercise are indisputable. What’s also beyond dispute is that strength training increases muscle mass and power. At ETH, we wanted to find out why people go to the gym, and what their goals are. To do this, we surveyed 430 people between the ages of 16 and 78. 67% were men, 33% were women.

The goals given, ranked here according to the highest level of agreement, ranged from becoming healthier and improving appearance, to increasing muscle mass and improving posture, to reducing excess fat, right through to socialising. Many of these goals place emphasis on changing the body.

The weekend pig-out

Researchers examined the influence of the «weekend lifestyle» on body mass over the course of a year-long study. They wanted to find out whether daily changes in diet or exercise habits during the week would cause the participants to gain weight – or be prevented from losing weight – on weekends [1]. Researchers recruited 48 participants aged 50 – 60 and assigned them randomly to three groups:

• Reduced calorie diet (CR), n = 19
• A comparable calorie deficit created through daily exercise (EX), n = 19
• Healthy lifestyle (HL) control group, n = 10

To allow data comparison, the control group was asked to modify their daily calorie intake without changing their exercise routine. In contrast, the EX group had to do more exercise, while keeping their calorie intake at its usual level. Accelerometers were used to monitor the participants while they exercised, while calorie intake was recorded with the help of a food diary. The participants were also provided with a scale and asked to measure their body mass. Every three months, these weigh-ins were conducted daily over a period of two weeks – after the participant had gone to the toilet in the morning, but before they’d eaten breakfast. The researchers gathered 437 of these measurements over the course of the study.

The results

Body mass

On weekdays, both CR and EX lost a significant amount of body mass. On weekends, however, the CR participants stopped losing body mass, while those in the EX group gained weight. The control group (HL) didn’t experience any significant weight changes, be it on week days or on weekends.

Energy intake

For all groups, energy intake was significantly higher on weekends than during the week. The CR group had the highest energy intake on Saturdays, while the EX group took in significantly more energy on both Saturday and Sunday compared to weekdays. For the HL group, Sunday was the day with the greatest energy intake compared to weekdays.

Exercise

The CR group did more exercise on weekends than during the week. No differences between weekends and weekdays were observed among the EX group. It was observed, however, that the HL group tended to exercise more on weekends.

A possible correlation doesn’t equal causation

It’s worth explicitly mentioning here that a possible correlation between energy intake and Monday gym crowds doesn’t imply causation. The best way to illustrate this is with a nonsense correlation. Looking at US spending on research, space, and technology from 1999 to 2009, this curve looks virtually identical over time to the curve for suicides in the USA by hanging, strangulation or suffocation. Obviously, there’s no connection between the two.

As a matter of fact, the EX group’s energy intake was higher on Saturdays and Sundays compared to weekdays. Drawing conclusions about the relationship between energy intake and the frequency of Monday gym visits isn’t scientifically sound – even if it is tempting.

If you want to avoid the crowds, it’s advisable to work out during off-peak hours. Those include early mornings, late evenings and Saturday and Sunday lunchtimes.

References

1. Racette SB, Weiss EP, Schechtman KB, Steger-May K, Villareal DT, Obert KA, et al. Influence of Weekend Lifestyle Patterns on Body Weight. Obesity. John Wiley & Sons, Ltd; 2008;16: 1826–1830. doi:10.1038/OBY.2008.320

Working days or weekends?