Can doing more exercise help older adults grow muscle when low volumes don’t work?

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Overview

Reference

Lixandrão, M. et al. (2024) 'Higher resistance training volume offsets muscle hypertrophy nonresponsiveness in older individuals.' Journal of Applied Physiology, volume 136, issue 2, pages 421-429.

Background

The amount of muscle growth from weight lifting varies a lot from person to person (people respond differently). Changing how weight lifting is done might affect these differences, but this is still unclear.

Objectives

The study looked at how changing the amount of resistance training affects muscle growth in people who do and don't respond to a small amount of resistance training (just one set). It also investigated how these changes affect muscle strength in these groups.

Methods

Eighty-five healthy older people (41 men and 44 women, with an average age of 68) took part in this study. Each person had one leg chosen randomly to do a single set of an exercise, and their other leg to do four sets of the same exercise. This exercise was the knee extension, done with enough weight that they could do 8 to 15 repetitions before needing to stop. They did these exercises twice a week for 10 weeks. To see the results, the authors used MRI scans and tested how strong each leg was in doing a knee-extension exercise with the maximum weight the participants could lift one time.

Results

Participants who didn't get stronger with just one set of knee extensions saw better results when they did more sets. They experienced muscle growth and got stronger when they followed a plan with greater resistance training volume. Those who did respond to one set also showed muscle growth, but especially when they did four sets of knee extensions. Maximum strength increased the same amount no matter how many sets participants did.

Conclusions

This study shows that doing more resistance training sets in a workout could be an easy and effective way to help older adults build muscle and get stronger, especially for those who don't see results from doing less training. Also, people who already benefit from less training could see even better muscle growth by increasing their training volume.

Limitations/Cautions

The authors couldn't control for some factors outside the study like sleep patterns, stress levels, or being more inactive, which might change how different subjects reacted to the study. However, the within-subject design - using the same subjects as their own control group - helped lessen this issue. They only included people who don't usually exercise to avoid differences in fitness levels affecting the results, but this means we can't say if their findings would apply to people who exercise more. They only measured muscle size in the middle of the quadriceps and didn't look at muscle growth along the entire muscle. This means we don't know if more muscle growth occurred elsewhere.

Detailed Review

Resistance training is a popular way to help prevent muscle loss and weakness that happen as people get older [1–4]. However, not everyone gets the same benefits from a standard resistance training program. Some people might see a small increase in muscle size from this kind of training, while others might see a much bigger improvement [5–11]. Researchers tend to refer to such people as "non-responders" and "responders," respectively.

Even though some people don't respond well to resistance training, changing the way they exercise could help. This means trying different kinds of movements and changing how much and how hard they exercise [12–15]. Research has shown that when people change how often or how intensely they do strength training, fewer of them have no response to the training [11]. One study found that increasing the amount of resistance training subjects did in each session was the only change that really helped build muscle more effectively. Changes like how hard the exercises were, how long breaks were, or the way the muscles moved didn't make a big difference [16].

Doing more exercise has been found to boost the activity of something called p70S6K, which is a part of a bigger system in our body called the mammalian target of rapamycin (mTOR) [17,18]. This suggests that how much we exercise could affect how well we respond to strength training. However, researchers still don't fully agree on whether doing more exercise changes how differently people's muscles grow with strength training. Differences in how the studies were done, the people in the studies, and how long the studies lasted, along with other natural body processes and outside influences like how well we sleep, what we eat, and how active we are, might also play a part in why people respond differently to resistance training - an issue present in studies comparing different people [5,6,9-11,19-22].

Using within-person study designs - experiments that focus on the same person - can reduce differences seen between different people. This way, we can understand better how changing the amount of resistance training affects each person. Resistance training helps improve physical function, such as muscle strength. However, how much strength improvement each person sees can vary a lot, too [5,23,24].

Thinking about the idea that changing how much resistance training we do might help people who aren't seeing muscle growth, we can also hope to see better muscle function. (like increased strength). Looking back at past studies, it seems people can get better from doing resistance training because they show at least one positive change from the training [23]. However, only a small number of people see benefits in from resistance training in all outcome measures.

Therefore, the authors of the study under review wanted to see how changing the amount of resistance training affects muscle growth and strength in people who do and do not respond well to a small amount of resistance training. They did this by having people train just one side of their body differently from the other side.

The resistance training program in the study under review used a knee extension machine. One leg did one set of knee extensions while the other leg did four sets, doing 8 to 15 repetitions per set with rest periods of 60 to 90 seconds between sets. To make sure the exercise was fair and didn't favour one leg over the other, participants switched the leg they started with each workout. In the first two weeks, they did all their exercises in sets of 12 to 15 repetitions. From the third week, they did 8 to 12 repetitions per set. To keep the number of exercises they could do the same, the weight they lifted was changed as needed. If they did more exercises than planned, the weight was increased next set; if they did fewer, the weight was decreased. The smallest change in weight was 1 kg. Participants did each set to form failure. An experienced trainer supervised all exercise sessions. The total volume of training was calculated by adding up all the exercises and the weight lifted over all sessions (sets x reps x weight)

The main findings showed that doing more resistance training helped make the quadriceps muscles bigger and stronger. Subjects saw more benefits doing 4 sets of knee extensions  instead of 1 set. However, the maximum weight subjects could lift increased the same, no matter how much training they did.

Some people might not respond well to resistance training because they're not doing enough of it. This means if they change how much exercise they do, it might help [12,13]. Actually, research shows that when people do more aerobic exercise, fewer of them fail to respond [15]. Also, if people who weren't responding well to resistance training start doing aerobic exercise more often, they improve their cardiorespiratory fitness [14]. It has been suggested that different kinds of strength training might help reduce the number of people who don't respond to exercise, eg., traditional weight lifting vs. power lifting 26].

The authors of the study under review found that doing more sets of resistance training (like 4 sets instead of just 1 set) helps people who didn't get stronger or have their muscles grow from doing less. This training made their muscles bigger and made them stronger when doing less didn't work. So far, only one other study looked at older people to see if more exercise helps grow muscles, but it didn't reach the same conclusions [27]. This inconsistency could be because of how the studies were set up differently or how they measured muscle growth like using different tools. The other study used a method (dual-energy X-ray absorptiometry) that's not as good at seeing changes in muscle size as the gold standard method mentioned in the study under review (MRI).

The findings of the study under review agree with another trial which shows that doing more exercises (18 sets a week compared to 6) works well for younger people [28]. All of this information tells us that doing more resistance training can  help older adults who don't usually respond to a low volume of training. This way, they can gain muscle and strength and fight off the usual muscle loss and weakness that come with getting older.

Even though doing more resistance training usually helps people get better results, a detailed analysis of individual data showed that 10 out of 51 non-responders (19%) did not get bigger muscles from exercising more. This matches what other researchers found in their study [27]. Natural body factors, like satellite cells and myonuclei content, might have a bigger impact on how much muscles grow compared to just changing how we train [21].

The people who didn't get better after doing 4 sets of exercises might not respond well to this kind of workout because their bodies have a hard time using certain processes needed for muscles to grow, such as stimulating key signalling pathways [10,12,29]. However, it's possible that they could still improve with more exercise, longer workout programs, doing different kinds of exercises together (like cardio and resistance training), changing their daily habits, or trying different food or health supplements [13,30–33]. This means more research is needed to understand this better.

In the study under review, 60% of people did not respond to the resistance training program, which is higher than in other studies where the non-response rate was between 2% and 50% [5–9,11,23–25,27,34,35]. We can't say for sure, but this might be because the resistance training program didn't involve enough exercise. However, other studies have shown that both too little and too much exercise can cause more people not to respond [11]. This seems to depend on the person, making it hard to find the perfect amount of exercise for everyone. These data show that while over half of the people who responded well to the program (17 out of 33, or 51%) saw their muscles grow more with greater volume of training, consistent with other research, 15% of people (5 out of 33) actually had poor reactions to more exercise [25,27,28]. This supports the idea that too much exercise stress can prevent muscle growth [11,25].

It's possible that some people might need small changes to how much they exercise, like having longer breaks, to get the best muscle growth from their workouts. This means it's better to have a training plan that fits each person's unique body needs instead of a one-size-fits-all approach. It's important to note that even though people respond differently to resistance training, those who are seen as good responders can get benefits from even a little bit of exercise. This shows that they are naturally very responsive to the mechanical stimulation they experience during exercise and can gain a lot from most training programs. Hopefully, upcoming research will look into how our bodies and how we feel can help make exercise plans better suited to each person's needs. Researchers should also explore how our bodies react differently to strength training at a deeper, biological level.

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