Untrained People Can Only Use 70% of Their Muscle Power. Here’s How Strength Training Unlocks the Missing 30% (No Size Needed)

Strength isn’t just about muscle size—and understanding this distinction could completely change your approach to training.

Popular anatomy educator Jonathan from the Institute of Human Anatomy recently broke down the science behind what actually makes someone stronger, and the findings might surprise anyone who assumes bigger muscles automatically equal more strength.

Because while muscle mass certainly plays a role, your nervous system might be the secret weapon you’ve been overlooking.

Here’s everything you need to know about building strength—with or without adding size—and why this adaptation might be the most important for longevity and functional fitness.

What Strength Actually Means (And How It Differs From Size)

Strength, at its core, measures your body’s ability to produce force during muscular contraction. It’s typically assessed through one-rep max testing—think seeing how much weight someone can squat just once.

But strength exists on a spectrum alongside other muscular adaptations, each requiring different training approaches.

The Three Primary Muscular Adaptations

Muscular endurance represents the lowest intensity contractions—think holding yoga poses or running half marathons. Training involves:

• 30-60% of one-rep max
• 15-20+ repetitions
• Bodyweight exercises held for extended periods
• High-volume, lower-intensity work

Hypertrophy sits in the middle range, focused purely on muscle size increases. Optimal training parameters include:

• 60-80% of one-rep max
• 8-12 repetitions
• High volume with multiple sets
• Multiple training sessions weekly

Strength demands the highest intensity contractions. Pure strength training requires:

• 80-100% of one-rep max
• 1-6 repetitions
• Lower volume compared to hypertrophy
• Longer rest periods between sets

Jonathan explains that transition zones exist between these adaptations. Training at 60-70% one-rep max bridges endurance and hypertrophy, while 70-80% bridges hypertrophy and strength.

Why Bigger Muscles Don’t Always Mean More Strength

Here’s where things get fascinating: bodybuilders often have significantly larger muscles than powerlifters, yet powerlifters frequently lift heavier weights.

The explanation lies in what creates muscle size during hypertrophy training.

Hypertrophy increases muscle size through multiple mechanisms—some contributing to strength, others not. Increased contractile proteins (actin and myosin) directly boost force production. However, hypertrophy also increases fluid content and glycogen storage within muscle fibers.

These latter adaptations add size but don’t translate to one-rep max strength. Instead, they support sustained performance across multiple repetitions and aid recovery between sets.

Your Nervous System: The Hidden Strength Multiplier

Understanding motor unit recruitment reveals how strength gains occur without size increases—and it’s absolutely mind-blowing.

How Motor Units Work

When you decide to contract muscles, signals originate in your brain’s motor cortex. Upper motor neurons carry these signals down your spinal cord, synapsing with lower motor neurons.

Each lower motor neuron controls multiple muscle fibers—anywhere from 6-10 fibers (for precise eye movements) to thousands (for large powerful muscles). This lower motor neuron plus all its controlled fibers forms what’s called a motor unit.

Here’s the crucial part: your body doesn’t automatically recruit all available motor units during contractions.

Studies have shown that untrained individuals can only voluntarily recruit about 70 to 85% of their motor units on demand depending on the muscle and the individual.

Your nervous system essentially doesn’t trust you with full control—it’s protecting soft tissues from potential damage through neuromuscular inhibition.

Training “Teaches” Better Recruitment

Strength training produces remarkable neurological adaptations:

• Increased motor unit recruitment: Trained individuals can voluntarily recruit 90%+ of motor units versus 70-85% in untrained people
• Faster recruitment speed: Motor units activate more quickly when needed
• Higher firing frequency: Recruited motor units fire more rapidly
• Better coordination: Improved efficiency in coordinating multiple muscle contractions

These adaptations allow significant strength gains without adding muscle mass—explaining why someone can lift considerably more weight after weeks of training despite minimal visible size changes.

Fast-Twitch Fibers: Your Strength Secret Weapon

Not all muscle fibers are created equal, and understanding fiber types explains why strength training becomes increasingly important with age.

Slow-twitch fibers contract with less velocity and force but resist fatigue exceptionally well—perfect for endurance activities.

Fast-twitch fibers contract with greater velocity and produce substantially more force but fatigue quickly—essential for strength and power.

Motor units are fiber-type specific, containing exclusively slow-twitch or fast-twitch fibers, never mixed. Your body recruits slow-twitch motor units first for lighter loads, only activating fast-twitch units when intensity reaches approximately 60-70% of one-rep max.

You’ll recruit the vast majority of fast-twitch fibers at 80-100% one-rep max—precisely the strength training zone.

Why Strength Training Becomes Critical As You Age

Here’s the sobering reality: fast-twitch muscle fibers are the first to atrophy with aging.

Even highly active older adults who maintain excellent cardiovascular fitness through walking, yard work, or endurance exercise rarely stimulate fast-twitch fibers during these activities. Without specific strength training, these fibers progressively waste away.

Jonathan notes he’s treated elderly patients who struggle getting up from chairs or off floors—and others who pop right up effortlessly thanks to consistent strength training.

Beyond basic functionality, strength training provides:

• Improved balance reducing fall risk
• Better bone density through progressive loading
• Enhanced sports performance across virtually all activities
• Functional carryover to daily tasks like lifting and moving objects
• Metabolic benefits supporting healthy body composition

How Much Strength Training Do You Actually Need?

Surprisingly little—which makes consistency far more achievable than most people realize.

Data shows that as little as about three to six hard sets per muscle group per week can be enough to maintain strength and produce modest improvements.

Jonathan shares his personal experience training for Spartan races, where trail running consumed most weekly training time. He maintained and even increased lower body strength with just one weekly session including squat and deadlift variations—three to four sets each.

For more ambitious strength goals, 6-10 hard working sets per muscle group weekly builds strength more rapidly.

Three Practical Training Splits

Option 1: Once Weekly Full-Body Strength

• Four main compound lifts: bench press, pull-ups, squat variation, deadlift variation
• Add accessory work like Bulgarian split squats and calf raises if time permits
• Requires absolute consistency—missing sessions dramatically reduces progress

Option 2: Twice Weekly Upper/Lower Split

• Upper day: bench press, pull-ups, shoulder press, rows
• Lower day: squat, deadlift, single-leg work, hamstring curls, hip thrusts
• Allows more volume and exercise variety

Option 3: Every-Other-Day Approach (Jonathan’s Personal Favorite)

This balanced routine alternates strength and cardio days:

Week 1: Monday upper, Tuesday cardio, Wednesday lower, Thursday cardio, Friday upper, Saturday hard cardio

Week 2: Monday lower, Tuesday cardio, Wednesday upper, Thursday cardio, Friday lower, Saturday hard cardio

Cardio includes zone-2 steady state (Tuesday/Thursday, 45-60 minutes) plus high-intensity 4×4 intervals (Saturday).

This approach checks multiple health boxes simultaneously—strength, cardiovascular fitness, and metabolic conditioning—making it ideal for general longevity-focused training.

The Bottom Line On Building Strength

Strength represents far more than aesthetic muscle size. While hypertrophy contributes to force production, neurological adaptations—improved motor unit recruitment, firing rates, and coordination—allow dramatic strength increases without corresponding size gains.

Training specificity matters enormously. Hitting 80-100% one-rep max for 1-6 reps optimizes pure strength development, recruiting fast-twitch fibers that endurance work leaves untouched.

Perhaps most importantly, maintaining strength becomes increasingly vital with age as fast-twitch fibers preferentially atrophy. Even minimal weekly volume—as little as one focused session—can preserve functional capacity, balance, and independence far into later years.

Whatever training split you choose, consistency trumps perfection. Your nervous system and muscles will adapt remarkably to regular progressive overload, building the resilient, capable body that supports both performance and longevity.