Muscle Strength and Growth – The Science and a Better Resistance Curve

Introduction

From so‑called “muscle confusion” workouts to miracle supplements, the fitness world is packed with noise. Strength training can feel overwhelming at times – there are endless programs, fads, and myths competing for attention.

That’s why I launched AgeFreeStrength and earlier posts like “Strength Training As We Age – An Introduction”. My goal has always been to explain why strength and muscle are critical as we get older, to share practical strategies for building them, and to challenge the misconceptions that hold people back.

This post takes the next step. We’ll look at how muscles really adapt and grow, what high‑quality research tells us, and why the way we apply resistance matters so much.

We’ll look at how AgeFreeStrength’s approach - combining portable tools, science backed optimal exercises, and efficient workout protocols - creates a better path to lasting strength and resilience.

Most importantly, this post is about clarity. I want to cut through the noise and give you simple, evidence‑based principles that work in real life – whether you’re training at home, in a hotel, or on the road.

What the Research Really Says

One of the most important findings in modern exercise science is that there is no single “best” way to lift.

Before diving in, it’s worth noting that the world of exercise science is overflowing with studies and opinions. Even some of the most respected experts have stated that studies need to be taken with a pinch of salt.

The problem is that studies rarely define the exact scenarios, criteria, and outcomes we as lifters are most interested in—and for every study you find, there’s often another that seems to contradict it.

It’s easy to cherry‑pick research to support almost any point of view, usually to grab clicks rather than provide clarity. Think of the endless YouTube thumbnails promising “a trick” or influencers swearing by miracle programs that supposedly “hack” muscle growth.

But there is one that cuts through the noise. A major meta‑analysis led by Dr. Stuart Phillips at McMaster University in 2017 pulled together 178 studies on strength and 119 studies on hypertrophy, covering more than 8,000 participants. The conclusion was clear:

All properly structured resistance training programs improved both strength and muscle growth and there was no statistically significant difference between them.

The surprising part? There was also no meaningful difference between heavy and moderate weight training – as long as the sets were performed with enough effort.

As Phillips summed it up:

“If you like lifting heavy weights, great. They work to make you stronger and grow muscle. But let’s be clear: lifting moderate weights, when lifted with high effort, do the same things. Especially with metabolic health. This has been shown countless times in men and women—older and younger.”

This flips the common gym myth on its head. Building strength and muscle isn’t about chasing the heaviest number on the bar. It’s about applying consistent effort, choosing movements that target the muscles effectively, and respecting intensity, safety, frequency and recovery.

Given the strength of that extensive study, it provides strong support for the AgeFreeStrength approach as follows:

• Time Efficient – less than half the time of traditional workouts
• Effective – our muscle physiology driven intensity, frequency and recovery protocols, based on Borge Fagerli’s Myo-Rep protocols – and our Advanced Resistance Curve Training (AD-Curve™ – see Section below)
• Joint Safe – our biomechanics driven optimal exercises, based on Moe Larbi and Doug Brignole’s Smart Training 365 platform.
• Portable – working out anywhere promotes consistency

So, with effort being the common denominator, how exactly do muscles adapt and grow? That’s what we’ll cover next.

How Muscles Grow and Get Strong

When you strip away the jargon, muscle growth and strength gains come down to four simple but powerful drivers.

Here’s a mildly scientific – but very summarized – look at each:

• 1. Muscle fiber recruitment and types of growth. Your muscles are made up of different types of fibers, from slow‑twitch endurance fibers to fast‑twitch power fibers. When effort is low, only a small percentage are activated. But as you push closer to failure, your nervous system recruits more and more motor units, especially those that control the larger fast‑twitch fibers that have the greatest potential for growth.
  
  That’s why those last challenging reps, known as effective reps, matter so much. These are the reps performed under the greatest fatigue and highest tension, where nearly all available motor units are firing. There are two main ways muscles grow:
  
  • Myofibrillar hypertrophy happens when the actual contractile proteins in the muscle – actin and myosin – multiply and thicken. This increases the density of the muscle fibers, leading to greater strength and a firmer, denser look.
    It is driven mostly by high levels of mechanical tension, typically when working with heavier loads or with moderate weights close to failure with a rest/pause protocol.
  • Sarcoplasmic hypertrophy is different. It refers to the increase in the fluid, glycogen, and energy substrates stored inside the muscle cell. This doesn’t add much to raw strength, but it increases muscle size and endurance.
    It is stimulated more by metabolic stress – the familiar “burn” you feel when pushing lighter/moderate weights close to failure.

Both types of growth matter. Myofibrillar adds contractile power, while sarcoplasmic adds volume and work capacity - as depicted in the image below. A well-rounded approach to training will stimulate both.

• 2. Progressive overload. Muscles adapt rapidly to the stresses you place on them. To keep improving, you need to provide a new challenge – whether that’s more resistance, extra reps, a slower tempo, or shorter rest periods.
  
  At the cellular level, progressive overload increases mechanical tension, boosts protein synthesis, and enhances the signaling pathways (like mTOR) that trigger muscle growth. This gradual progression forces the body to adapt by getting stronger and growing muscle.

Here’s a personal note: since I was born in 1959, and having worked out for decades, simply holding on to the muscle and strength I have is in itself a form of progression. Every workout is, in a sense, fighting off sarcopenia - the age‑related loss of muscle that so many accept as inevitable. 

In my view, that was progress worth celebrating - until I discovered AD-Curve™(see next Section) and, in my senior years, have actually increased muscle and strength.

• 3. Recovery. Training is the spark, but recovery is where the growth actually happens. During rest, your body repairs tiny micro‑tears in the muscle fibers, making them stronger and thicker.
  
  What’s often misunderstood is that muscle damage itself doesn’t promote growth – it actually delays it. The body has to spend resources repairing the damage before it can begin building new muscle tissue.
  
  Put simply, that’s why the balance of intensity and recovery is critical. Ideally, you want to hit the sweet spot of supercompensation: training again once recovery is optimal and your body has adapted by building a little extra capacity but not waiting so long that you lose momentum.
  
  Sleep and relaxation supply the recovery environment, and stress management keeps the system in balance.
  
  Supercompensation
  
  The graph below depicts the intensity and time recovery curves with the green curve being optimal. To progressively raise the baseline, we should train the muscle group again at the peak of supercompensation – but when is that?
  
  It depends on the intensity (weight, reps, proximity to failure), volume, your age and how you are feeling (sleep, stress etc), and the muscle group. Smaller muscle groups such as the biceps require less recovery time than large muscle groups such as the quads.
  
  With the AgeFreeStrength moderate weight rest/pause (Myo-Reps) protocol, we prefer our 2-way workout split routines done every other day, for a 3 to 4 day ‘recovery sweet spot’ of muscle group supercompensation.
  

• 4. Nutrition. Food provides the raw materials for growth and recovery. Adequate protein delivers amino acids for muscle repair and synthesis, carbohydrates replenish glycogen for energy, and healthy fats support hormones involved in muscle development. Hydration also plays a role in performance and recovery.
  
  Nutrition is another area full of myths that I will delve into in a dedicated post.

Together, these factors explain why consistent training with the right balance of effort and recovery produces results at any age. The optimal exercises and protocols we use at AgeFreeStrength are designed specifically to maximize these drivers—giving your body the best chance to get stronger, healthier, and more resilient.

The AD-Curve™ Advantage

Advanced Resistance Curve Training (AD-Curve™) is the AgeFreeStrength method of combining portable cable resistance with bands to better match the body’s natural strength curve. The result is smoother, safer loading, and higher-quality reps with muscle engagement across the full range of motion.

Every exercise has what’s called a resistance curve – how the external load on your muscles changes through the range of motion.

Most experts agree that the ideal resistance curve should align with the muscle strength curve: the natural pattern of how strong a muscle is at different joint angles. In simple terms, muscles can produce their greatest force when elongated in the early phase of a movement, remain strong through the mid‑range, and then lose force as they shorten toward the contracted position. This is explained by the length–tension relationship of muscle fibers: when shortened, the overlap between filaments reduces their ability to generate force.

However, studies also show that training in the contracted range – where the muscle is shortened – does contribute to strength and hypertrophy, although the effects tend to be more localized compared to lengthened‑range loading.

Here’s a quote from Borge Fagerli, one of the world’s most respected trainers and the creator of the Myo-Rep protocol. For those of you interested in a deep dive into the science of muscle growth and the mindset to sustain it, I strongly recommend his book Myo-Reps The eBook (no affiliation).

“Your combined cable + band approach makes perfect biomechanical sense. By providing constant baseline tension and then overlaying resistance to maintain challenge as leverage improves, you’re getting meaningful resistance throughout the entire range – constant load where you’re strongest (bottom) and increasing load to compensate for decreasing leverage (top) – something traditional setups rarely achieve.” — Borge Fagerli

It’s worth clarifying that different muscles (fan‑shaped, fusiform, etc.) do have slightly different strength curves, but the overall principle holds true. Likewise, pushing and pulling movements both follow this same length–tension relationship, even though angles and leverage can vary.

• Free weights overload only at certain angles. For example, in a dumbbell curl, due to gravity and physics, the tension drops off near the top when your forearm is vertical – right when your biceps could still be working.
• Bands are the opposite: light at the start, but increasingly heavy as they stretch, which can overload the end range while under‑challenging the beginning.
• Cables provide more consistent tension, but typically not enough to counteract the target muscle de‑loading through the range of motion.
• Specific exercises need to be done to train the contracted range eg: biceps concentration curls.
• Some machines use cams to vary the resistance curve, but we aren’t covering machines in this website as they are not portable.

Through plenty of trial and error, I found that the Pump Cables alone, in some exercises, don’t provide enough resistance. That led me to combine my AgeFreeStrength portable equipment in a way that produced more effective, higher‑quality reps than either tool on its own.

By pairing the Unitree Pump cable system with resistance bands, the two offset each other’s weaknesses. The Pump provides baseline cable tension across the range, while the bands overlay extra resistance exactly where the direct load to the working muscle would otherwise ease off. Anchoring them side by side makes the movement smoother and keeps the muscle under load from start to finish.

The images and videos in the next section show the AD‑Curve in action.

The key takeaway is simple:

In summary, the AD‑Curve delivers better quality reps and is an AgeFreeStrength hallmark - aligning the resistance curve with the strength curve through the full range of motion. 

Why does this matter, especially as we age? Because:

• It’s safer on the joints – no jarring shifts in load.
• It provides consistent and extended tension, ensuring that every rep counts across the full range of motion.
• It creates better muscle activation – more effective reps in every set while reducing workout time.
• When paired with our portable equipment and routines you get time efficient and quality workouts – anywhere.

AD-Curve™ In Practice

Applying AD-Curve is simple and flexible. In practice it means using cable resistance and bands together to maximize the quality of every rep via an optimal resistance curve.

The AgeFreeStrength and AD-Curve method is branded for total portability, hence the combination of our lightweight portable equipment that we take with us while flight/hotel travelling, vehicle touring/camping and at homes.

As described in our post Working Out While Touring and Camping, our portable equipment includes Unitree Pump Pros and various layered latex loop resistance bands. However, the AD-Curve can be applied by combining bands with home or commercial gym cable machines also – by experimenting with band anchor points on or adjacent to the specific equipment.

The AD-Curve protocol is similar in concept to adding chains or bands to barbells and dumbbells – to increase the target muscle load through the range of motion. What sets the Age Free Strength AD-Curve apart is the totally portable cables/bands combination.

Other portable cable equipment options include the Shogun Flex (essentially Unitree Pumps under a different brand name) and the MaxPro Air. We prefer the Unitree Pump Pros because they are compact, light, very portable and provide concentric and eccentric load – whereas the MaxPro only provides concentric resistance – but with some imagination, all types of cable or free weight resistance equipment can be used in conjunction with bands.

Interested in Unitree Pump Pros? Click here for an additional 20% discount

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The Discovery Phase

I first stumbled on the AD-Curve method by accident during one of our early camping tours while experimenting with our portable equipment. The exercise that ignited the method was the Converging Cable Chest Press. One of the limitations with the Unitree Pumps is the 20kg per unit maximum resistance—which wasn’t enough for me with the Converging Press.

I considered combining the Pumps (up to 40kg resistance) for a unilateral press, but the stability of the bilateral version makes it the optimal exercise. Initially, I used either the Pumps or the Bands, but then I decided to combine them. The difference was a game changer.

This led to the realization that the resistance curve created by the combo was a better match for the natural muscle strength curve—especially as physics starts to de‑load resistance applied to the muscle through the full range of motion.

Equipment and Setup

One of the many advantages with our portable equipment is the flexibility it provides with the AD-Curve setup and deployment.

With the variety of bands available in terms of their loop length, strength and the exercise setup distance from the anchor point, an almost limitless cables/bands AD-Curve resistance is achievable.

Since the post on Working Out While Touring and Camping, where I showcased our portable equipment, I have purchased additional bands to add to our mobile gym and AD-Curve routines.

All of our bands are layered latex loop bands for durability, flexibility and safety. We now have 2 of each of the following – tabulated below with the standard un-shortened lower and upper resistance (noted as ‘Res’). Shortening the bands by looping them at anchor points raises their starting resistance, since it reduces working length and increases baseline tension. Doubling them over doubles the resistance.

Brand	Color	Lower Res	Upper Res
Serious Steel 32″	Orange	1kg	7kg
Serious Steel 32″	Purple	2kg	16kg
Serious Steel 32″	Red	5kg	23kg
X3 41″	White	5kg	23kg
X3 41″	Light Grey	11kg	36kg

We set the Cables and Bands up as per the image below. For the Converging Chest Press, I anchor both together more than shoulder width apart. I use S-Hooks over the roof rack as the Pump Cable anchors and loop tie the bands such that the cable handles are longer than the bands. This ensures the bands are stretched at the start of the range of motion, adding to the initial load.

Exercise Demonstration and Resistance Curve Example

As noted above, it was the Converging Chest Press that initiated the AD-Curve method.

With the Converging Chest Press I combine the Unitree Pump Pro cable resistance with the Serious Steel 32″ Purple bands. The bands anchoring position and initial stretch adds approximately 6kg to each arm at the start of the exercise and increases through the range of motion.

The Age Free Strength AD-Curve Converging Press

Our totally portable AD-Curve Converging Chest Press is biomechanically and muscle physiologically optimal—here’s why:

• With cables and bands, the resistance direction is from the anchor points to the handles – not just vertical gravity as with free weights.
• The anchor points are positioned wider than shoulder width to enhance the initial stretch.
• We have solid lower back stability – in our case by propping against our vehicle.
• We keep our elbows bent to help maintain the effective load to the target muscle through the range of motion – which is enhanced further by the AD-Curve cables/bands combination.
• When paired with our rest/pause protocol we get maximum muscle stimulation in minimum time.

Demonstration

Resistance Curve Comparisons

The chart below shows the effective resistance curve comparison. ‘Effective resistance’ refers to the load directly applied to the target muscle, in this case the pectorals (chest), through the range of motion – not the linear resistance.

Without the AD-Curve, load to the target muscle diminishes as the arms start to straighten.

In the image below note the shape of the effective resistance curves with the following notes:

• Although the Dumbbell Bench Press is a preferred chest exercise due to the early phase loading and the converging movement, the effective load to the target muscle drops away at the end with the arms straightened relative to the line of resistance being vertical (gravity).
  The ubiquitous Barbell Bench Press is less effective with the hands locked in position. Note that neither dumbbell nor barbell exercises are in the Age Free Strength arsenal due to their lack of portability – they are included in the chart only for the resistance curve comparison.
• The Converging Cable Press is better with the line of resistance aligned with the movement – but cables alone don’t fully offset the effective load drop as the arms straighten.
• The AD-Curve Converging Press provides a superior effective load through the full range of motion thanks to the cables and bands combination.
• For the resistance curve comparisons, I set the resistance to match the AD-Curve Converging Press I do – starting at approximately 26kg.

Closing Thoughts

The AD‑Curve method isn’t about adding complexity – it’s about making every rep more effective by matching resistance to your body’s natural strength curve. Whether you’re training at home, in the gym, travelling or out on the road, this simple combination of cables and bands gives you an edge that dumbbells, barbells, bands or cables alone can’t match.

This post is designed to introduce the concept. For members, we dive deeper with detailed routines, exercise breakdowns, and demonstrations showing how AD‑Curve principles can be applied across all major muscle groups.

And this is only the beginning. A forthcoming eBook will expand AD‑Curve training systematically across all muscle groups, with structured routines, progressions, biomechanics diagrams, and practical applications.

If you’re serious about training smarter, not just harder, and want portable, sustainable, and biomechanically sound methods—then the AD‑Curve is your next step.