Exercise for Aging Explained: Unveiling HIIT vs. voluntary wheel running (VWR)

A recent study published in Frontiers in aging compared the effects of high-intensity interval training (HIIT) and voluntary wheel running (VWR) on physical function in aging mice. Both exercise types were found to be effective in mitigating age-related decline. HIIT showed some advantages in younger mice, but both were equally beneficial in older mice. Exercise helped preserve muscle mass and improve physical function in both age groups. HIIT was more time-efficient than VWR. The study highlights the importance of regular physical activity for maintaining health and independence throughout life, regardless of age or exercise preference.Title: Exercise in Aging: Comparing High-Intensity Interval Training and Voluntary Wheel Running in Mice

Key points

1. Exercise is beneficial at any age: Both HIIT and VWR were effective in mitigating age-related decline in physical function.

2. Exercise type may depend on age: HIIT showed some advantages over VWR in younger mice, but both were equally effective in older mice.

3. Exercise preserves muscle mass: Both exercise types helped preserve muscle mass in aging mice.

4. Exercise improves physical function: Both exercise types improved physical function, including treadmill performance and grip strength.

5. HIIT is more time-efficient: HIIT was found to be more time-efficient than VWR.

6. It's never too late to start exercising: Even older mice who started exercising later in life experienced benefits.

7. Personalization is important: The best exercise type may vary between individuals, so it's important to find an activity you enjoy.

The Role of Exercise in Aging: Comparing High-Intensity Interval Training (HIIT) and Voluntary Wheel Running (VWR)

As the global population ages, the importance of maintaining physical function to ensure quality of life and independence becomes increasingly apparent. Regular exercise is a well-established intervention to combat age-related physical decline, but questions remain regarding which types of exercise are most beneficial at different stages of life. A recent study sought to address this by comparing the effects of two popular endurance exercise models—high-intensity interval training (HIIT) and voluntary wheel running (VWR)—in mice at different ages. The results offer valuable insights into how different exercise modalities can help preserve physical function across the lifespan.

Study Overview

The study focused on male C57BL/6 mice, a commonly used model for aging research. The researchers divided the mice into two age groups:

1. Adult mice: Starting at 6 months old (comparable to humans in their early to mid-20s) and ending at 10 months (similar to early middle age in humans).

2. Older adult mice: Starting at 22 months old and ending at 26 months (equivalent to humans in their early 70s).

The mice were randomly assigned to one of three groups:

1. High-intensity interval training (HIIT): A structured exercise regimen involving short bursts of intense activity followed by periods of rest or lower-intensity exercise.

2. Voluntary wheel running (VWR): A self-paced exercise model where mice had free access to a running wheel.

3. Sedentary control (SED): Mice that did not engage in any structured exercise.

The researchers hypothesized that HIIT, due to its structured and intense nature, would be more effective than VWR in improving physical function and exercise capacity.

Measuring Outcomes

To evaluate the effects of the exercise interventions, the researchers employed several key measurements:

1. Comprehensive Functional Assessment Battery (CFAB): A composite scoring system that includes:

• Voluntary wheel running: assesses volitional exercise and activity rate.

• The treadmill test: measures endurance.

• Rotarod test: evaluates overall motor function.

• Grip meter: Assesses forelimb strength.

• Inverted cling test: Measures whole-body strength and endurance.

2. Body composition: tracked using EchoMRI to measure fat and lean mass.

3. Muscle wet mass: Measured after the training period to assess muscle preservation.

4. Plantar flexor torque: Specifically measured in adult mice to evaluate lower limb strength.

Key Findings

The study yielded several intriguing findings, some of which were unexpected.

In the adult mice, the results revealed that all groups, including those that exercised, experienced a decline in overall function (as measured by CFAB scores) as they aged from young adulthood to early middle age. However, the two exercise groups—HIIT and VWR—significantly mitigated this functional decline compared to the sedentary group.

Key Findings in Adult Mice:

HIIT vs. VWR: HIIT showed some advantages over VWR in maintaining physical function. Specifically, the HIIT group outperformed the VWR group in the rotarod test, which measures overall motor function, and in the treadmill test, which assesses endurance. Additionally, HIIT was more effective in mitigating the overall functional decline (as indicated by CFAB scores).

Strength Differences: Interestingly, VWR mice demonstrated stronger forelimbs compared to HIIT mice. This could be attributed to the nature of wheel running, which likely emphasizes forelimb engagement more than HIIT.

Body Composition: Both exercise types had similar effects on body composition, with no significant differences between the groups in terms of fat and lean mass.

Older Adult Mice (22-26 months)

In the older adult mice, the results were somewhat surprising. Contrary to the researchers' initial hypothesis, both HIIT and VWR provided similar overall benefits in this age group. Both exercise groups either maintained or improved physical function, while the sedentary group showed a decline.

Key Findings in Older Adult Mice:

HIIT vs. VWR: In older mice, both exercise models were equally effective in preserving physical function. However, there were some specific differences:

VWR mice exhibited stronger forelimbs compared to HIIT mice, which is consistent with the results seen in the younger mice.

HIIT mice showed significant improvements in treadmill performance compared to the VWR group, indicating better endurance in this group.

Muscle Preservation: Both exercise types helped preserve muscle mass in older mice, particularly in the soleus muscle, which is critical for posture and locomotion. This suggests that exercise, regardless of the type, may have an age-reversing effect on muscle mass.

Overall Benefits: The findings underscore that even in older age, consistent physical activity—whether through structured HIIT or more self-paced VWR—can help maintain or even improve physical function.

Time Efficiency

One of the notable aspects of the study was the comparison of time efficiency between HIIT and VWR. The HIIT regimen was much more time-efficient than VWR:

HIIT: The mice engaged in 6-10 minutes of intense activity, followed by 6-7 minutes of lower-intensity recovery, warm-up, and cool-down, three times per week.

VWR: The mice spent an average of 13-17 hours running on wheels over four days per week.

This finding is particularly relevant for humans, as time constraints are often cited as a barrier to regular exercise. HIIT offers a way to achieve similar or better results in a fraction of the time compared to more moderate-intensity, self-paced activities.

implications for Exercise and Aging

The results of this study have several important implications for our understanding of exercise and aging.

1. Exercise Type Matters, But Age is a Factor

The study suggests that the effectiveness of different exercise types may depend on the age of the individual. For younger adults, HIIT might be more effective in preserving physical function as they approach middle age, offering advantages in motor function and endurance. However, in older adults, both HIIT and VWR were similarly beneficial, indicating that any form of consistent exercise can help maintain or improve physical function as we age.

This highlights the importance of tailoring exercise programs to the individual, taking into account their age and specific needs. For younger adults, a more structured, high-intensity exercise program like HIIT might be ideal, while older adults may benefit just as much from a more moderate, self-paced activity like VWR.

2. The "Use It or Lose It" Principle

The study reinforces the well-known "use it or lose it" principle. As we age, our bodies naturally experience a decline in physical function. However, regular physical activity can significantly slow this process. Even though all groups, including those that exercised, showed some functional decline from young adulthood to early middle age, those that engaged in regular exercise fared much better than the sedentary group.

This underscores the importance of maintaining an active lifestyle throughout life. The earlier we start exercising and the more consistently we maintain that habit, the better our chances of preserving our physical capabilities as we get older.

3. It's Never Too Late to Start

One of the most encouraging findings of this study is that older adult mice, who had been sedentary for most of their lives, still showed significant improvements or maintenance of physical function when they began exercising. This aligns with human studies that demonstrate significant health benefits even for people who start exercising later in life.

The message here is clear: it's never too late to start exercising. Even if you've been inactive for years, beginning a regular exercise routine in your 60s, 70s, or beyond can help maintain your physical function and independence.

4. Time Efficiency of HIIT

In our busy modern world, time is often a limiting factor when it comes to exercise. The study highlights the time efficiency of HIIT compared to voluntary wheel running. Mice in the HIIT group achieved similar or better results with much less time spent exercising. For humans, this suggests that incorporating short bursts of high-intensity exercise into our routines could be an effective way to maintain fitness, especially for those with limited time.

However, it's important to note that the best exercise is the one you'll actually do consistently. For some, a longer, more moderate-intensity activity like VWR might be more sustainable, while others might prefer the efficiency of HIIT.

5. Different Exercises, Different Benefits

While both HIIT and VWR provided similar overall benefits in older mice, there were some differences in specific outcomes. For example, VWR led to greater improvements in forelimb strength, likely due to the gripping action required during wheel running. On the other hand, HIIT led to better improvements in treadmill performance, suggesting enhanced endurance.

This indicates that different types of exercise may offer specific benefits. A well-rounded exercise routine that incorporates various activities could be ideal for overall health and function, allowing individuals to reap the benefits of different types of exercise.

6. The Importance of Personalization

The variability in individual results, particularly among older adult mice, suggests that the effectiveness of different exercise types may vary from one individual to another. This highlights the importance of personalized exercise prescriptions, especially for older adults.

In a human context, this means that while any exercise is generally beneficial, finding the right type and intensity of exercise for each individual could optimize the benefits. Factors such as personal preferences, existing health conditions, and fitness levels should all be considered when designing an exercise program.

Limitations and Future Directions

While this study provides valuable insights, it also has several limitations that should be acknowledged:

1. Gender Specificity: The study only included male mice, so potential sex differences in response to exercise were not explored. Future research should include female mice to determine if there are any significant differences in exercise response between sexes.

2. Wheel Size: The small size of the running wheels may have limited the amount of voluntary running, especially for larger mice. Future studies could use larger wheels or different voluntary exercise models to see if the results differ.

3. Exercise Intensity: The intensity of the HIIT program for older mice may have been overly cautious, potentially limiting the maximum benefits observed. Future studies could explore different intensities of HIIT in older populations to determine the optimal level of intensity.

4. Pandemic Restrictions: Due to pandemic-related restrictions, some data collection for the older sedentary group was limited. This may have affected the robustness of the results.

Future Research Directions

To build on these findings, future research could explore several interesting directions:

1. Sex Differences: Investigate potential differences in exercise response between male and female subjects.

2. Longer-Term Studies: Conduct studies that span a longer period to assess how different exercise types affect both lifespan and healthspan.

3. Exercise Intensities: Explore the effects of varying exercise intensities, particularly in older populations, to identify the most beneficial intensity levels.

4. Health-Specific Outcomes: Examine how different types of exercise impact specific aspects of health, such as cognitive function, cardiovascular health, or metabolic function.

5. Molecular Mechanisms: Study the molecular mechanisms behind the benefits of different exercise types to better understand how exercise influences aging at the cellular level.

This study sheds light on the role of different types of exercise in maintaining physical function across the lifespan. The key takeaways are:

• Exercise is beneficial at any age, but the type of exercise that provides the most benefit may change as we get older.

• For younger adults, high-intensity interval training may be particularly effective in maintaining physical function.

• For older adults, both high-intensity training and more moderate, self-paced exercise can provide significant benefits.

• It's never too late to start exercising—even previously sedentary individuals can see improvements in physical function by becoming more active.

• High-intensity interval training can provide similar benefits to longer, moderate-intensity exercise in a much shorter time, which could be particularly useful for time-constrained individuals.

As we continue to age as a population, understanding how to maintain physical function and independence throughout life becomes increasingly crucial. This research contributes to our knowledge in this area, providing insights that could help shape exercise recommendations and interventions for people of all ages. Remember, the best exercise is the one you'll actually do consistently, so find activities you enjoy and make them a regular part of your routine. Your future self will thank you!

Journal reference:

Pajski, M. L., Byrd, C., Nandigama, N., Seguin, E., Seguin, A., Fennell, A., & Graber, T. G. (2024). Endurance exercise preserves physical function in adult and older male C57BL/6 mice: High intensity interval training (HIIT) versus voluntary wheel running (VWR). Frontiers in Aging, 5, 1356954. https://doi.org/10.3389/fragi.2024.1356954

Image credit:https://www.bariatric-surgery-source.com/image-files/middleview_images/bariatric-exercise-benefits-m.png

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