Boost Metabolism with Interval Training
Age and Metabolism
As We Age, Our Metabolism Changes
It’s definitely not your imagination! As we age, our metabolism changes. A combination of factors contributes to create a perfect storm.
Some of these include:
Stress and Cortisol:
When we are stressed for long periods of time, our cortisol levels can spike. Elevated cortisol is linked to:weight gain
high blood pressure
fatigue
changes in mood
irritability
flushed face
thinning skin
difficulty concentrating
insulin resistance
Loss of Fast Twitch Fibers:
Aging typically leads to a decrease in the number and size of fast twitch muscle fibers, which can contribute to reduced strength, power, and metabolic rate. With fewer fast twitch fibers, metabolism may slow down, making weight management more challenging unless targeted exercises are employed to maintain or even enhance these fibers. VERY few healthcare professionals, and even personal trainers mention this, but I’ve seen first hand how this is an enormous factor. Don’t worry, we’re going to explain what the heck these are in this lesson. 🙂
Lack of Sleep: One study in JAMA mentions something we know to be true: when we don’t sleep well, we gain weight. It’s a recipe for issues.
People who sleep less:
crave fattier foods
see a spike in blood pressure
have decreased Leptin levels, which means you don’t feel as full (even if you are), which means you eat more
have increased Ghrelin levels which makes you feel hungry
It’s so important to try to manage our stress, get enough sleep, and understand the changes in our body as a baseline.
Your Muscle Type Matters
Muscle Fiber Types: Muscle fibers are categorized into two main types based on their contraction speed, endurance, and metabolic pathways. Everybody has a mix of all muscle fiber types. However, we typically have more of one type overall in our teens and early adult years. Here are the types (again, a simplification, but good for reference):
Slow Twitch (Type I) Muscle Fibers:
Characteristics: These fibers are designed for endurance activities and are resistant to fatigue.
Function: Slow twitch fibers rely primarily on aerobic metabolism (oxidative phosphorylation) to produce energy, making them efficient for activities like prolonged walking, jogging, and maintaining posture.
Color and Appearance: They are red in color due to their rich myoglobin content, which stores oxygen for sustained contraction.
Fast Twitch (Type II) Muscle Fibers:
Type IIa: These fibers have characteristics between slow and fast twitch, offering a balance of endurance and power.
Type IIb (or IIx): These are the fastest contracting fibers but also fatigue the quickest.
Characteristics: Fast twitch fibers contract quickly and forcefully but fatigue faster compared to slow twitch fibers.
Function: Fast twitch fibers primarily use anaerobic metabolism (glycolysis) to generate energy, making them well-suited for explosive movements like sprinting, jumping, and lifting heavy weights.
Color and Appearance: They are pale or white in color due to lower myoglobin content and fewer blood vessels.
Muscle fiber type is heavily influenced by the aging process. The percentage of type II “fast twitch” muscle fibers tend to decline with age. The way our muscles behave in general also changes as we age.
Here are a few of the things that happen to our muscles as we get older:
Reduction in Muscle Fiber Size and Number
Muscle Atrophy: Aging is associated with sarcopenia, a condition characterized by the loss of muscle mass and strength.
Fast Twitch Fiber Vulnerability: Fast twitch muscle fibers are particularly vulnerable to atrophy compared to slow twitch fibers due to their reliance on anaerobic metabolism and higher energy demands.
Loss of Motor Units: Motor units (a motor neuron and all the muscle fibers it innervates) that control fast twitch fibers can decrease in number with age, further contributing to muscle weakness and reduced power output.
Changes in Muscle Composition:Shift Towards Slow Twitch Fibers: There is evidence suggesting that aging leads to a shift in muscle fiber composition, with a relative increase in slow twitch fibers and a decrease in fast twitch fibers.
Impact on Performance: This shift can impair explosive movements, decrease speed, and reduce the ability to generate quick bursts of force needed for activities like climbing stairs, lifting heavy objects, or even maintaining balance.
Why Interval Training Boosts Metabolism
With the decline in “fast twitch” (type II) muscle fibers, comes a decline in muscle performance and metabolism.
Here are a few of the the things that happen:
Metabolic Impact:
Decreased Metabolic Rate: Fast twitch fibers play a significant role in basal metabolic rate due to their higher energy consumption during exercise and at rest.
Weight Management Challenges: A decline in fast twitch fibers can contribute to a slower metabolism, making weight management more difficult unless countered by appropriate exercise and dietary adjustments.
Insulin Sensitivity: Fast twitch muscle fibers play a role in glucose metabolism and insulin sensitivity, which decline with age and can contribute to metabolic disorders like type 2 diabetes if not counteracted through exercise.
Functional Limitations:
Daily Activities: Reduced fast twitch muscle function can impact daily activities requiring strength, agility, and balance, such as getting up from a chair, carrying groceries, or playing with grandchildren.
Risk of Falls: Weakness in fast twitch fibers increases the risk of falls, fractures, and other injuries, which are more prevalent in older adults, especially women.
Muscle-Bone Interaction: Fast twitch muscle fibers contribute to bone health through mechanical loading and stress on bones during intense physical activities.
Osteoporosis Risk: Women are particularly susceptible to osteoporosis, and the loss of fast twitch muscle fibers can exacerbate bone density loss if not addressed through weight-bearing exercises.
Age Related Decline in Fast Twitch Muscle Fibers
With the decline in “fast twitch” (type II) muscle fibers, comes a decline in muscle performance and metabolism.
Many women are told to focus on exercises such as yoga, or walking, or slow-moving strength training as we age. Unfortunately none of these exercises increase fast-twitch muscle fibers. They certainly don’t challenge the muscles as we age, which means you can workout every day and not see a lot of progress. Sound familiar?
Sometimes we need to “rile things up” to make progress. (Note from Julie here: When I started sprinting one minute at 5MPH on a treadmill, then 30 seconds to 1 minute at 8MPH, I made more progress in one month than 3 months of running at 6MPH). This is about 80% of my capacity.
Focusing on fast twitch muscle activation leads to faster improvements in fitness and weight loss, especially as we age, because it challenges our muscles.
According to Dr. Stacy Sims, an author and professor who dislikes cardio classes like OrangeTheory, because as she explained on a recent Andrew Huberman episode:
“It puts women squarely in moderate intensity…they leave classes feeling absolutely smashed…actually training doesn’t work for you because it’s putting you in a state of intensity that drives cortisol up but its not a strong enough stress to invoke the post-exercise growth hormone and testosterone responses that we want to dampen that cortisol…
We hear this women who are 40+ should not do high intensity work…well actually they shouldn’t do moderate intensity…we want true high intensity work, which is 1-4 minutes of 80% or more, or if you’re doing sprint interval it’s full gas for 30 seconds or less.”
Here’s a bit about the science of how it works, and what we mean by “short burst” exercise.
Short Bursts Exercise Includes:
Explosive Movements: This often includes exercises that require quick and powerful movements, such as sprints, jump squats, or plyometric exercises like box jumps.
Fast Twitch Activation: These explosive movements demand rapid force production, which primarily recruits fast twitch muscle fibers to generate power and speed.
Short, Intense Intervals: Sometimes called HIIT, or High Intensity Interval Training, involves short bursts of high-intensity exercise followed by periods of lower intensity or rest. During the high-intensity intervals, fast twitch muscle fibers are recruited to meet the sudden demand for strength and power.
Compound Movements: Many interval training exercises involve compound movements that engage multiple muscle groups simultaneously. This integration challenges coordination and balance while effectively recruiting a larger proportion of fast twitch muscle fibers across various muscle groups.
How Short Bursts Activate the Fast Twitch Muscles:Anaerobic Metabolism: Fast twitch fibers predominantly rely on anaerobic metabolism (glycolysis) to produce energy quickly, which is essential for sustaining high-intensity efforts during intervals.
Muscle Fiber Recruitment: Over time and with consistent training, interval sessions train the neuromuscular system to recruit and activate fast twitch muscle fibers more efficiently.
Increased Fiber Utilization: Regular interval training can lead to adaptations in muscle fibers, including increased size and improved oxidative capacity of fast twitch fibers, enhancing their ability to sustain high-intensity efforts.
Increases Metabolic Demand: The intense nature of interval training not only activates fast twitch fibers but also elevates heart rate and oxygen consumption significantly.
Continual Fat Burning After Exercise: This metabolic demand leads to an increased post-exercise oxygen consumption (EPOC), where the body continues to burn calories and fat to restore oxygen levels and repair tissues, further enhancing weight loss and fitness gains.
As always, be sure to speak with your doctor before starting an exercise regimen, and always listen to your body. It’s ok to stop a workout in the middle. It’s ok to leave an exercise class, and it’s ok to not work out for days on end if you’re not feeling it.
Exercises That Activate Fast-Twitch Muscle Fibers
As always, be sure to speak with your doctor before engaging in an exercise regimen!
Key Takeaways: When you focus on exercises that activate your fast twitch muscle fibers, you may achieve faster and more noticeable results compared to traditional low-intensity workouts typically recommended with aging. Everyone is different, and results take time no matter what exercise regimen. But trying something different may very well be the catalyst required to change your body.
High-Intensity Interval Training (HIIT):
Description: HIIT involves alternating short bursts of intense exercise with brief periods of rest or low-intensity recovery.
Fast Twitch Activation: HIIT workouts recruit fast twitch muscle fibers to meet the demands of high-intensity efforts such as sprinting or rapid movements.
Sprint Intervals:
Description: Sprint intervals involve maximal effort sprinting for short durations followed by periods of active recovery. [Note from Julie, as I mentioned before, my own regimen includes 60 seconds to 90 second extremely fast sprinting–like 8MPH or faster, followed by 5-6MPH slower run, for about 20-25 minutes. This is my regimen that works for ME and it gives me a real mental health boost as well with a playlist I created that alternates between angry Industrial music and 80s pop ;)).]
Fast Twitch Activation: Sprinting activates predominantly fast twitch muscle fibers due to the explosive nature and high force production required.
Resistance Training:
Description: Resistance exercises involve using external resistance (e.g., weights, resistance bands) to challenge muscles.
Types of Exercises: Plyometrics (e.g., jump squats, box jumps), explosive lifts (e.g., kettlebell swings, power cleans), and resistance band exercises can effectively target fast twitch muscle fibers.
How to Get Started
As always, be sure to speak with your doctor before engaging in an exercise regimen!
Your new exercise regimen might be tough to begin with.
Be sure to listen to your body!! Progress with working out takes discipline and it isn’t supposed to be easy. That said, it should not hurt. Working with a Certified Personal Trainer can help reduce your risk of injury. We recommend finding someone who specifically knows how to work with women as we age, and specifically understands the science behind muscle fiber type and metabolism.
As a general rule, we would recommend:
Fast Twitch Exercises: Choose exercises that emphasize explosive movements, such as sprints, jumping jacks, burpees, or kettlebell swings, to effectively target fast twitch muscle fibers.
Progression: Start with shorter intervals and gradually increase intensity and duration as fitness levels improve to continually challenge fast twitch muscle fibers.
Recovery: Adequate rest between intervals allows for partial recovery of fast twitch muscle fibers, enabling higher quality effort in subsequent intervals.
Challenges and Adaptations:
Initial Challenges: Transitioning to high-intensity exercises can be physically demanding initially, but the body adapts by improving cardiovascular fitness, muscle strength, and endurance.
Long-Term Adaptations: Consistent training that emphasizes fast twitch fibers can lead to significant improvements in overall fitness, making daily activities easier and more enjoyable.
Full Mind-Body Integration: You’ll see faster results when you:Incorporate exercise into your daily routine –we schedule it in as if it is a meeting.
Find community resources, social support, and professional guidance to keep you motivated and accountable.
Blend holistic approaches to aging well and improving your metabolism, including nutrition, stress management, and sleep quality.
The decline of fast twitch muscle fibers with age, particularly in older women, underscores the importance of targeted exercise interventions to maintain muscle function, metabolic health, and overall quality of life.
By understanding these physiological changes, you can make informed decisions about your fitness routines, and boost metabolism in a healthy way.
