How Strength Training Changes Body Composition
- Tony Palladino
- Jan 16
- 12 min read
Strength training is one of the most effective ways to improve your body composition. It helps you build muscle, lose fat, and maintain a healthier metabolism, especially as you age. Unlike cardio or dieting alone, strength training preserves muscle while reducing fat, reshaping your body in a sustainable way.
Key takeaways:
Muscle vs. Fat: Strength training increases lean muscle mass, which burns more calories even at rest, while helping to reduce body fat.
Midlife Benefits: Women in their 30s and 40s face muscle loss and fat redistribution due to hormonal changes. Strength training combats these effects.
Resting Metabolism: For every kilogram of muscle gained, resting metabolic rate rises by about 21 calories/day.
Fat Loss Efficiency: Combined with a calorie-controlled diet, strength training can reduce body fat by up to 3.8% while preserving muscle.
Long-Term Health: It lowers risks of diabetes, osteoporosis, and age-related muscle loss.
Strength training is more than a workout - it's a tool for lasting physical and metabolic health. Start with simple movements like squats, lunges, and push-ups, and focus on consistency over intensity. Even two sessions per week can make a difference.
The Problem: How Aging Changes Body Composition
Muscle Loss and Slower Metabolism
Starting at age 30, muscle mass begins to decline at a rate of 3%–8% per decade, and this rate doubles to 5%–10% after age 50. Skeletal muscle plays a crucial role in burning calories, even when you're at rest. So, when muscle mass decreases, it slows down your metabolism, making it easier to gain fat.
For instance, women aged 25–44 tend to gain around 1.1–2.2 pounds annually, and midlife women typically add about 1.5 pounds and 0.3 inches to their waistline each year. Beyond weight gain, lower muscle mass increases the risk of health issues like type 2 diabetes, falls (2.1 times higher risk), and bone fractures (2.7 times higher risk) in post-menopausal women.
This gradual muscle loss creates the foundation for more noticeable body composition changes, especially as hormonal shifts come into play.
How Hormonal Changes Affect Your Body
On top of muscle loss, hormonal changes - particularly declining estrogen levels - intensify the way fat is stored in your body. These changes often begin in your 30s and 40s, but they become especially pronounced during menopause, which typically occurs between ages 45 and 55. As estrogen levels drop, your body doesn’t just gain fat - it redistributes it.
"The decline in estrogen levels has detrimental effects on body composition, such as an increase in fat mass (FM), a decrease in MM [muscle mass], strength, and bone mineral density (BMD)." - BMC Women's Health
One of the most noticeable shifts is the movement of fat from the hips and thighs to the abdomen. This increase in abdominal fat includes inflammatory visceral fat, which poses higher health risks. These hormonal-driven changes in fat distribution not only alter appearance but also have a significant impact on metabolic health.
Movement and Strength Training to Improve Metabolic Health
How Strength Training Helps You Lose Fat
Strength training does more than just build muscle - it changes how your body uses energy, making it a powerful tool for improving body composition.
Increasing Your Resting Metabolic Rate
One of the standout benefits of strength training is its ability to preserve your metabolism during weight loss. When you lose weight through dieting alone, you often shed both fat and muscle, which can slow your metabolism. Strength training helps counter this by preserving muscle mass, which is essential for maintaining your resting metabolic rate (RMR).
Take, for instance, a study conducted at the University of Alabama at Birmingham. Researchers followed 94 premenopausal women through a weight loss program where participants lost about 26 pounds (12 kg). Women who incorporated resistance training into their routine experienced a much smaller drop in their resting energy expenditure - just 44 kcal/day. In contrast, those who focused on aerobic exercises saw a decrease of 76 kcal/day, while non-exercisers experienced a decline of 103 kcal/day. As Gary R. Hunter, the lead researcher, explained:
"Resistance training during weight loss may have a positive effect on subsequent weight maintenance by preserving muscle mass, strength fitness, and REE."
Here’s another compelling fact: for every kilogram of muscle you gain, your resting metabolic rate increases by about 21 calories per day. Unlike cardio, which only burns calories while you’re moving, muscle keeps working for you around the clock.
But the benefits of strength training don’t stop at metabolism - it also enhances how your body burns fat.
Improving Your Body's Fat-Burning Ability
Strength training doesn’t just rev up your baseline metabolism; it also fine-tunes how your body uses energy. It improves insulin sensitivity by activating GLUT-4 proteins, which help transport glucose into your muscle cells. This means stronger muscles can absorb more glucose, reducing the amount of excess fat your body stores and encouraging the use of existing fat for energy.
Another advantage is the "afterburn effect", or EPOC (excess post-exercise oxygen consumption). Resistance training can keep your metabolic rate elevated for hours - or even days - after a workout. This extended calorie burn, combined with improved fat oxidation during exercise, makes strength training particularly effective at targeting visceral fat. This type of fat, often found around the abdomen, is linked to metabolic diseases.
When combined with a moderate calorie deficit, strength training has been shown to reduce body fat percentage by 3.8% and decrease total fat mass by about 12 pounds (5.3 kg), all while preserving lean muscle. This means the weight you lose comes from fat, not muscle, which is crucial for achieving lasting changes in body composition.
How Strength Training Builds Muscle
Strength training helps develop new muscle, effectively countering the natural muscle loss that often begins for women in their 30s and 40s.
Using Progressive Overload to Build Muscle
The cornerstone of building muscle is progressive overload - a methodical increase in weight, repetitions, or overall training volume over time. By consistently challenging your muscles with resistance beyond what they're accustomed to, they adapt and grow stronger. The goal isn’t to lift the heaviest weight right away but to gradually push your limits.
Studies reveal that women participating in a full-body resistance training program for approximately 15 weeks gained about 3.3% in lean body mass - equivalent to around 3.2 pounds (1.45 kg) of muscle. These participants also saw a 25% rise in upper body strength and a 27% boost in lower body strength. The key? Training at an intensity of 70% to 80% of their one-repetition maximum, completing about three sets of ten repetitions, three times a week.
Gina Harney, NASM-CPT and founder of Fitnessista.com, emphasizes the importance of strength training for women in their 30s:
"When a woman is in her thirties, strength training becomes even more important to promote muscle density and metabolic function."
To implement progressive overload, you might increase the weight on your squats by 5–10% or add one or two extra repetitions to each set. Another effective technique is slowing down the lowering (eccentric) phase of an exercise, which increases the time your muscles are under tension - a proven way to stimulate growth without necessarily adding more weight.
These gradual adjustments pave the way for building strength and achieving a more sculpted, defined look.
Why Muscle Creates a Toned Appearance
The toned look many women aim for isn’t the result of endless light-weight, high-repetition exercises. Instead, it comes from increasing muscle size while simultaneously reducing body fat. As muscles grow, their cross-sectional area and thickness increase, creating more definition and shape.
Resistance training not only builds muscle but also helps lower body fat percentage. Research shows it reduces body fat by an average of 1.46% while building lean muscle mass. This combination of more muscle and less fat is what creates visible muscle definition. As noted in the Sports Medicine Journal:
"Resistance training is the gold standard exercise mode for accrual of lean muscle mass."
For most women, adding about 3.2 pounds of muscle over 15 weeks results in a more sculpted and defined physique - not excessive bulk.
Overall Body Composition Changes and Key Benefits
Strength training does more than just help you lose fat and gain muscle - it reshapes your body in a way that creates lasting, meaningful change.
Physical and Mental Changes
The physical impact of consistent strength training is undeniable. By building lean muscle, it specifically targets visceral fat, which is linked to serious health risks. But the benefits don't stop at the surface.
As your muscles grow stronger, everyday tasks become easier. This improvement in functional fitness not only enhances your physical capabilities but also boosts your confidence and energy levels in daily life. Jennifer W. Bea, PhD, from the University of Arizona, highlights how this works:
"Resistance training may contribute to increased energy expenditure during activities of daily living, as well as intentional physical activity, due to increased energy burning muscle mass and increased ease of physical activity."
For many women, sticking with a strength training program leads to feeling more empowered and in control of their bodies. This mental transformation often spills over into other areas of life, enhancing self-confidence and a sense of capability. These physical and mental changes create a solid foundation for long-term health.
Long-Term Health Benefits
The advantages of strength training extend well beyond visible results. Regular resistance training is a proven way to reduce the risk of chronic diseases.
For women in their 30s and 40s, maintaining bone health is crucial. Strength training applies the mechanical forces needed to preserve bone mineral density, significantly lowering the chance of osteoporosis and fractures later in life. On a metabolic level, it improves insulin sensitivity, helps prevent type 2 diabetes and cardiovascular disease, and combats sarcopenia - the age-related loss of muscle mass and strength that accelerates with hormonal changes.
Strength training also helps counter midlife weight gain and fat redistribution. Without intervention, women in their 40s typically gain about 1.5 pounds (0.7 kg) per year and see an annual increase of 0.7 cm in waist circumference. The Bone Estrogen Strength Training (BEST) study, conducted at the University of Arizona between 1995 and 2004, tracked 122 postmenopausal women over six years. Those with high attendance (around 64%) maintained their weight and regional fat levels, while those with low attendance experienced significant weight gain and increased trunk fat. As lead researcher Jennifer W. Bea, PhD, stated:
"Resistance training is a viable long-term method to prevent weight gain and deleterious changes in body composition in postmenopausal women."
Practical Strength Training Solutions for Lasting Results
Strength training can reshape your body and improve your health without requiring endless hours at the gym. By focusing on effective strategies, you can build muscle, lose fat, and maintain these results over time.
Starting with the Basics
To get the most out of your workouts, focus on compound movements like squats, deadlifts, and push-ups. These exercises target multiple muscle groups, making them efficient and effective. For beginners, emphasizing large lower-body muscle groups can help improve metabolic health and overall longevity.
Start with bodyweight exercises - such as squats, lunges, push-ups, and planks - to perfect your form before incorporating weights. A balanced routine should include core movement patterns like pushing, pulling, squatting, lunging, twisting, pressing, and gait work. Instead of trying to do it all, stick to 4–5 well-executed exercises per session.
Research shows that dedicating just 1–2 hours per week to weightlifting, split into 2–3 sessions of 20–30 minutes each, can significantly lower the risk of obesity. Once you establish a routine, consistency becomes the key to seeing long-term results.
Consistency Over Perfection
A six-year study of postmenopausal women revealed that those with a 64% attendance rate in strength training sessions maintained their body composition and avoided weight gain. In contrast, women with just 2.5% attendance saw significant increases in weight and trunk fat. This highlights that showing up regularly matters more than achieving perfect intensity every time.
Interestingly, research on middle-aged women suggests that strength gains can be similar whether training at 50% or 75% of one-repetition maximum. As Lindsay Brin, an Exercise Science Specialist at Moms Into Fitness, notes:
"The brain doesn't necessarily perceive the number on the dumbbell, it perceives the load or tension".
To keep progressing, gradually increase the weight, the number of reps, or reduce rest periods - this principle is known as progressive overload. A helpful rule for selecting the right weight is the "2-3 reps to failure" guideline: choose a load that leaves you 2–3 reps shy of failure by the end of your set. Even beginners can see noticeable changes by performing just 5–6 sets per muscle group each week.
Toned By Tony: A Supportive Solution
For those looking for a structured approach, Toned By Tony (https://tonedbytony.com) offers a program tailored to women in midlife. The Fit & Functional program combines functional strength training, flexible nutrition strategies, and personalized coaching. Delivered through a user-friendly app, it tracks your progress and adapts to your schedule.
What makes this program stand out is its focus on achieving results with the minimum effective effort. Customized workout plans fit seamlessly into your lifestyle, while weekly accountability check-ins and 1-on-1 coaching help you stay on track. Tony’s philosophy emphasizes consistency over perfection, encouraging you to build strength and confidence without resorting to punishing routines. This approach helps you overcome challenges like burnout and maintain a positive mindset as you work toward your goals.
Conclusion
Strength training offers more than just physical transformation - it plays a key role in maintaining metabolic and hormonal balance. It helps reshape body composition by reducing fat and building lean muscle, which is especially important for women in their 30s and 40s. This practice can counter common issues like annual weight gain and the accumulation of visceral fat.
The secret to success lies in consistency. Long-term research shows that regular strength training helps maintain weight and fat levels, while inconsistent participation often leads to weight and fat increases. Jennifer W. Bea, PhD, from the Arizona Cancer Center, highlights the value of this approach:
"Resistance training is a viable long-term method to prevent weight gain and deleterious changes in body composition in postmenopausal women."
These insights emphasize the importance of creating sustainable habits. Celebrate progress - whether it’s lifting heavier weights or noticing strength improvements - and remember that muscle gain might offset fat loss on the scale. Even committing to just two sessions a week can deliver meaningful results.
Focus on building a routine that feels achievable and boosts confidence. By prioritizing strength and consistency, you’ll set the foundation for long-term health and well-being.
FAQs
How does strength training impact your body composition compared to cardio?
Strength training does more than just help you shed weight - it reshapes your body by building lean muscle and reducing fat. While cardio burns calories during the workout, it doesn’t do much to increase muscle mass. On the other hand, resistance training promotes muscle growth, which revs up your metabolism. The result? You burn more calories even when you’re not moving, making strength training a powerful tool for long-term fat loss and weight management.
Another key difference is that cardio can sometimes lead to both fat and muscle loss. Strength training, however, preserves muscle, which is especially crucial for women in their 30s and 40s. Keeping muscle mass not only supports bone health and functional strength but also contributes to a more toned and defined look. Programs like Toned By Tony’s Fit & Functional are designed to make progressive strength training accessible, helping women enjoy these benefits without needing to carve out hours from their busy lives.
What are the best strength training exercises for beginners to improve body composition?
For women in their 30s and 40s new to strength training, starting with straightforward exercises can be a great way to build muscle, support fat loss, and boost overall fitness. Here are a few beginner-friendly moves to consider:
Overhead Press with March: Hold light dumbbells and press them overhead while marching in place. This exercise helps strengthen your shoulders and improves balance.
Hammer Curls: Keep your palms facing each other as you curl dumbbells. This targets your biceps and forearms while being easy on the elbows.
Dumbbell Lunges: Step forward into a lunge while holding light dumbbells at your sides. It's great for building leg strength and enhancing stability.
Beginner Deadlift: With dumbbells in hand, hinge at your hips and lower the weights toward the floor, then return to standing. This move works your glutes, hamstrings, and lower back.
Aim for 2–3 sessions per week, performing 1–2 sets of 10–12 repetitions for each exercise. Start with light dumbbells (5–10 lb) or even household items, focusing on proper form before increasing the weight. This simple routine is low-impact, targets all major muscle groups, and requires minimal equipment - perfect for beginners looking to gain strength and confidence.
How does strength training support women during menopause?
Strength training can be a game-changer for managing the hormonal shifts that happen during menopause. It helps preserve and rebuild lean muscle mass, which plays a key role in supporting hormones like insulin and testosterone - both of which naturally decline as we age. By doing so, it can increase your resting metabolic rate, reduce visceral fat, and improve blood sugar control. These effects can help tackle common menopause symptoms such as weight gain, fatigue, and mood swings.
On top of that, regular resistance training helps combat the loss of muscle and bone density, which is a frequent concern during this stage of life. These benefits go beyond just physical strength - they also help reduce inflammation and improve overall metabolic health. Programs like Toned By Tony are a great fit for women seeking effective, sustainable solutions. With a mix of functional strength training, flexible nutrition, and personalized coaching, they’re designed to help you feel stronger and more confident as you navigate this transformative phase.
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