Light or heavy weights? Fast leg training helped older adults either way

With age, muscles lose not only strength but, even more, power: the ability to produce force quickly. Power is what you need to get up from a chair, climb stairs or catch yourself when you trip, and losing it raises the risk of falls and disability. Training that asks people to push as fast as they can, called power training, is a known way to slow that loss.

Power has two ingredients: how much force a muscle can produce and how fast it can move. Some coaches of young athletes tailor training to whichever ingredient is weaker. A randomized controlled trial at KU Leuven in Belgium tested whether that idea helps older adults. In short: it did not make a difference to power or to everyday tasks, although the two kinds of training built different things.

What they did

• Profiling: 80 healthy, independent adults aged 65 or over (and, for reference, 60 adults aged 20–35) did fast pushes on a leg press against several loads. From this the team estimated each person's maximum force and maximum speed, and compared the older adults with the young group.
• Who had which weak spot: about three in four older adults (59 of 80) were classed as having a "velocity deficit", meaning their speed had fallen further behind the young than their force had. Only 4 had a force deficit, too few to study, so the trial included only the velocity group.
• The trial: 57 of them were randomly assigned to 12 weeks of supervised leg-press training twice a week. One group trained at light loads, 40% of the heaviest weight they could lift once, which is matched to a speed weakness (28 people). The other trained at heavy loads, 80%, deliberately not matched to it (29 people). Both pushed each repetition as fast as possible and stopped a set once their speed dropped.
• Measured: leg power, force and speed at the start, after 6 weeks and after 12 weeks, plus everyday tests: grip strength, fast walking over 10 metres, standing up from a chair, a get-up-and-walk test, a jump and climbing six stairs.

What they found

• Different training, different gains. The light-load group got faster: their maximum speed rose clearly, while their maximum force did not change significantly. The heavy-load group got stronger: their maximum force rose, but their speed did not. Both differences between the groups were statistically significant.
• Same power. Maximum leg power rose in both groups by a similar amount, about 32 watts (8.6%) with light loads and 36 watts (9.7%) with heavy loads. Most of the gain came in the first six weeks.
• Same everyday benefit. Both groups improved on almost all the physical tests over 12 weeks, and there was no significant difference between them on any test.
• Wide variation. How much people gained differed a lot from person to person, and tailoring the load did not narrow that spread.
• Well tolerated. More than 90% of sessions were attended, and participants rated the training as very enjoyable and doable (9.2 out of 10). Four people dropped out, three of them because of pain in the hip or leg.

What to keep in mind

• No non-training group. The trial compared two kinds of training with each other. The authors note that without a group that did not exercise, some of the improvement could come from practice at the tests or other factors.
• Fit volunteers. Participants were healthy and already scored high on a standard test of physical function, so there was little room to improve. The results may not apply to frailer older adults.
• The "weak spot" label depends on the method. The authors stress that their cut-off is a study-specific rule, not a diagnosis. Partly for statistical reasons, the method was more likely to label people as speed-deficient, so the three-in-four figure is not an estimate of how common this is in older people.
• Small and short. 52 people were analysed at 12 weeks, and nobody with a force deficit could be tested. Whether tailoring helps over longer programs is unknown.
• Lab tests are not daily life. Better scores in controlled tests do not necessarily mean better functioning at home.

Why it matters

For older adults starting power training, this trial suggests that the exact load matters less than doing the training at all: light and heavy loads each improved power and physical tests over three months, by different routes. The authors conclude that the load may be better chosen by a person's preferences, abilities and needs than by a force-speed profile, and point out that light-load training is a practical option when equipment is limited. Longer studies, and studies in less fit people, are needed to see whether tailoring pays off later.