For older adults' muscles, the time of day of strength training made no clear difference

Should you lift weights in the morning or the evening? Muscle strength rises and falls over the day, and muscle cells have their own internal clocks, so it seems plausible that timing matters. A trial from the University of Basel tested a personalized version of that idea in older adults, and found no advantage.

With age, people lose muscle mass and strength, starting around the fifth decade of life and faster later. Severe loss is called sarcopenia, and it makes falls, frailty and disability more likely. Strength training is one of the best-established ways to slow this down. Exercise guidelines say how often, how hard, how long and what kind of exercise to do, but not at what time of day. Earlier studies compared fixed times (often early morning against late afternoon) and found little difference. The Basel team suspected that this was because people differ in when they are strongest.

What they did

The researchers recruited healthy adults aged 60 to 80 who lived independently. Each person first did strength tests on four different days, each time at a different hour: 8:00, 12:00, 16:00 or 20:00. The test was a "mid-thigh pull": pulling as hard as possible on a fixed bar, which measures whole-body strength. From these tests the team found each person's strongest (peak) and weakest (trough) time of day.

108 people were then randomly assigned to three groups:

• Peak group: trained at their personal strongest time of day.
• Trough group: trained at their personal weakest time.
• Control group: kept their usual lifestyle, with no training.

The two training groups did the same supervised program for 12 weeks: twice a week, five strength exercises (leg press, chest press, deadlift, cable row and squat) with three sets each, pushed to the point where another repetition was impossible; and once a week, 30 minutes of moderate cycling. The participants and the trainers did not know which training group was the "peak" one, and the person measuring results did not know anyone's group.

The main outcome was strength on the mid-thigh pull; the team also measured grip strength and the muscle mass of arms and legs with a body scan.

What they found

• People really were stronger at certain times. Before training, people's strongest time was most often the afternoon or evening, and their weakest most often noon or morning. On average, they were about 11% stronger at their peak than at their trough, but this ranged from 1% to 34% between individuals.
• Both groups stuck with it. They attended over 90% of the strength sessions.
• Strength went up in all groups over the 12 weeks.
• No difference between peak and trough training. The adjusted differences between the two groups were close to zero for whole-body strength, grip strength and muscle mass.
• No winning clock time. Comparing those who happened to train at 8:00, 12:00, 16:00 or 20:00 also showed no consistent pattern.
• Against the untrained group, too, differences were small, according to the paper; the details are in its supplementary tables.

There were no serious adverse events related to the training. Of the 15 people who dropped out, nine cited muscle or joint complaints.

What to keep in mind

• Healthy, fit volunteers. Participants were relatively strong for their age, so the authors caution that the results may not apply to frail people, people with sarcopenia or several illnesses, or people living in care homes.
• Only 12 weeks, of which the first two were for getting used to the exercises. Muscle growth is slow in older adults, and small differences may have been too subtle for the body scan to pick up.
• Peak times are estimates. Each person's best and worst time came from one four-day series of tests, and for people whose strength barely changes over the day there was little difference to exploit.
• Uneven dropouts. More people left the peak group (14%) than the other groups (5% each), most of them women. The groups also ended up with unequal shares of men and women.
• Small trial. It was designed to detect a moderate difference. Smaller effects cannot be ruled out, but the authors argue that with estimates this close to zero, any missed effect is unlikely to matter in practice.

Why it matters

Many people wonder whether there is a best time of day to exercise. In this carefully run trial in healthy older adults, matching strength training to one's personal best time gave no measurable advantage, and no clock time stood out. The authors conclude that older adults can train at whatever time suits them, which they suggest may help people stick with it.