In my 15 years of training people in person, along with six years coaching clients online, I’ve encountered one set of questions more than any other;

Should I lift heavy or light for muscle growth?

How many reps build the most strength?

Do I always need to train near my one-rep max?

These age-old questions have challenged lifters of all backgrounds—whether young or old, strong or recovering from pain, beginners or seasoned athletes. As a NASM-certified personal trainer and someone who has been lifting for 18 years, I’ve guided countless individuals through these dilemmas.

At our training studio, we work with a diverse range of clients and understanding how to balance training load and volume is key to helping people achieve their best results safely and sustainably.

Resistance training (lifting weights) primarily produces three key effects:

• Strength refers to the ability to exert maximal force.

• Hypertrophy involves an increase in muscle size due to the growth of muscle fibres.

• Muscular endurance is the ability of a muscle to sustain repeated contractions
  over time. (we won’t go into endurance in this article).

So how do training loads impact the effects of resistance training?

Let’s see what the scientifically approved publications say.

In 2017, Brad Schoenfeld—known for his work on muscle growth—published a large meta-analysis (a study that analyzes and pools data from many studies on the same topic) comparing low-load and high-load resistance training.

The study reviewed 21 high-quality trials and remains highly influential in strength science.

Schoenfeld is known for methodical, high-quality work that bridges the gap between science and the weight room, and this paper is no exception.

Since 2017, this paper’s been cited over 500 times in scientific journals and is still showing up in new studies — a clear sign that it’s made a major impact in the hypertrophy research space.

It offers one of the most reliable summaries of the evidence on how different training loads affect strength and muscle growth.

To answer the first question: Does lifting heavy actually lead to greater strength gains?

The results showed heavier loads produce greater strength gains, in 1RM performance.

“Gains in 1Rep Max (1RM) strength were significantly greater in favor of high vs low load training” (Schoenfeld,2017)”
​

The chart above shows a forest plot of the 14 studies comparing how effective low-load (under 60% of your 1-rep max) versus high-load (over 60% of your 1-rep max) training is for increasing 1-rep max (1RM) strength.

In every study, the black square falls to the right side of the dotted line — meaning the statistics consistently favoured high-load training for building strength. The further right the square, the stronger the effect.

The overall effect size (ES) — a statistical measure of how strong the difference is — was 0.58. That’s considered a moderate effect, which in plain terms means lifting heavier weights leads to noticeably greater strength gains.

The 95% confidence interval ranged from 0.28 to 0.89. That means if this research were repeated 100 times with different groups of people, we could expect the true effect to fall within that range 95 times out of 100 — a medium to large effect in favor of heavy lifting.

To answer the second question: can you build just as much muscle with lighter weights?”

​“Changes in measure of muscle hypertrophy were similar between conditions. Findings indicate that maximum strength benefits are obtained from the use of heavy loads while muscle hypertrophy can be equally achieved across a spectrum of loading ranges” (Schoenfeld,2017).

Figure 4 above shows a forest plot of the 10 studies comparing how effective low-load (under 60% of your 1-rep max) versus high-load (over 60% of your 1-rep max) training is for increasing muscle hypertrophy.

Unlike the strength results, the black squares here are scattered — some favoring high-load training, some favoring low-load, and others sitting near the middle. This indicates there’s no clear winner when it comes to building muscle size between lifting heavy or lighter weights.

The overall effect size (ES) was just 0.03, which is essentially no meaningful difference between low- and high-load training for hypertrophy.

The 95% confidence interval ranged from -0.16 to 0.22, meaning if this research were repeated 100 times with different groups, the true effect would likely fall within that range 95 times out of 100 — reinforcing that the difference in muscle growth between the two training styles is insignificant.

The authors also noted:

“Our findings on the topic are primarily based on untrained subjects”

So what about trained lifters? Would the results be different with experienced individuals?
​
One of studies in the meta- analysis did include trained subjects — Schoenfeld (2015) — found similar outcomes. Let’s take a closer look.

Schoenfeld (2015) compared low- vs. high-rep resistance training in 18 trained individuals over 8 weeks. One group did 8–12 reps per set, the other 25–35, both to failure. All other training variables were identical. Participants trained full-body three times a week, with strength, endurance, and muscle growth in the biceps, triceps, and quads measured before and after.

Strength Results:

1RM Bench Press: The high-load (HL) group improved by 6.5%, while the low-load (LL) group improved by 2%. Though HL showed more progress, the 6.5% vs. difference wasn’t significant enough to claim HL was better.

1RM Back Squat: HL improved by 19.6%, while LL improved by 8.8%, with a statistically significant difference favouring HL.

Hypertrophy Results:

Biceps: HL grew by 2.5 mm (5.3%) vs. LL’s 3.7 mm (8.6%), with no significant difference.
Triceps: HL grew by 2.7 mm (6.0%) vs. LL’s 2.3 mm (5.2%).
Quads: HL increased by 5.3 mm (9.3%) vs. LL’s 5.2 mm (9.5%). Again, no significant difference.

Summary of Schoenfeld (2015)

Strength: High-load training led to greater strength gains in the squat, with slight improvements in the bench press, but the difference wasn’t significant enough to favor HL universally.

Hypertrophy: Both high- and low-load training led to similar muscle growth, with no clear advantage for either, despite slight differences in muscle thickness measurements.

In another study on trained lifters (Schoenfeld, 2016), This was not part of the 2017 meta-analysis. 26 men were split into two groups with an average of 4 years lifting experience in one group and 5 years of experience in the second.

The 2 Studies on Experienced Lifters:
Heavy group: 2–4 reps per set
Moderate group: 8–12 reps per set

Both groups followed the same full-body workout plan, training three times per week for 8 weeks. Exercises included flat barbell press, military press, wide-grip lat-pulldown, seated cable row, back squat, leg press, and leg extension. All sets were performed to failure at a controlled tempo (1 second up, 2 seconds down) with 2-minute rest intervals. Weights were adjusted to keep reps within the target range. Progress was measured using 1-rep max tests (bench press and back squat) and muscle thickness via ultrasound scans before and after.

Strength Results:

1RM Bench Press: Both groups got stronger, with the heavy-weight group showing a slight advantage, but the difference wasn't significant.

1RM Back Squat: The heavy-weight group showed significantly greater strength gains than the moderate group.

Hypertrophy Results:

Arm Muscles (elbow flexors and extensors): Both groups saw growth, but moderate weights led to slightly better results, especially for the back of the arm.

Thigh Muscles (side of the thigh): Both groups saw growth, but the moderate-weight group had more significant gains.

The 2 Studies on Experienced Lifters
Schoenfeld (2015): Compared 8–12 reps (HL) vs. 25–35 reps (LL).
Schoenfeld (2016): Compared 2–4 reps (HL) vs. 8–12 reps (LL).

Strength: Both studies showed strength gains, but heavier loads were more effective, especially for back squats.

Bench press strength was also slightly better with heavy lifting, though not always significantly. These findings align with untrained individuals, reinforcing that heavier loads generally build maximal strength more effectively.

Hypertrophy: The 2015 study found similar muscle growth across high and low-load groups. The 2016 study showed better hypertrophy with moderate loads (8–12 reps) than with very heavy loads (2–4 reps). Importantly, the "moderate" group in 2016 used the same rep range as the HL group in 2015, suggesting both studies support the 8–12 rep range as optimal for muscle growth.

The slightly lower hypertrophy in the 2–4 rep group may be due to reduced training volume, emphasizing volume’s key role in muscle development.

And this is exactly what the next review suggests.

In a 2025 systematic review, Fernandes and his team examined 10 studies on how low loads specifically affect muscle growth and strength.

The main findings were:

A. Volume load using 20% 1RM appears to influence muscle hypertrophy to the same extent as 80% 1RM.

B. High-load (80% 1RM) may be superior for strength gains compared to low-load (20% 1RM).

Volume load is the total amount of weight lifted during a workout, calculated by multiplying the weight used, reps, and sets.

“These findings support the idea that volume load plays a key role in muscle growth, regardless of load. As Fernandes notes, “In summary, it seems that the volume load can become an interesting point for muscle hypertrophy, because the studies demonstrate that low loads (20, 30% or 40% 1RM) were able to induce similar muscle hypertrophy when compared to high loads (80% 1RM) in equivalent volumes.”

The review also cites Lasevicius et al. (2022), who suggested that

"training to muscle failure does not provide additional strength or hypertrophy benefits compared to stopping short of failure—provided total training volume is equal. However, due to the limited number of well-controlled studies, further research is needed for definitive conclusions."

Much of the research comparing low and high loads involves training to momentary concentric failure to elicit adaptations.

Momentary concentric failure means lifting a weight until you can’t complete the upward part of the movement anymore.

However, I align more with Lasevicius.

Pushing every set to failure isn’t necessary. In practice, I’ve found staying 1–2 reps shy of failure and occasionally taking sets to failure, not on every set, works just as well. (as long as you progressively increase total volume over time). It helps manage fatigue especially with lower body training.

Load and Fatigue: Think of It as a Spectrum

On one end, maximal strength work (1-rep max or near-max) will get you stronger quicker but is highly fatiguing and requires longer recovery. On the other end, lighter loads (30–50% 1RM) are less taxing, allowing more volume—ideal for muscle growth.

There’s a trade-off between load and reps. You can’t lift very heavy and do many reps for long without overtaxing your body.

Schoenfeld (2016) highlighted that by saying “high RT volumes combined with heavy loads may chronically overstress joints, soft tissue, and the central nervous system (CNS), increasing risk of overtraining and injury,” originally noted by Fry and Kraemer (1997).

​If you’re managing pain or have injury concerns, I’d like to remind you that many of the low-load training studies performed 20+ reps, sometimes up to 35 reps. High rep sets still produce strength gains (though less than heavy loads) and similar muscle growth when total volume is matched. This means you can use lighter weights, reduce joint stress, and build muscle at your own pace. They key is doing it patiently with an injury and not rushing your body before its ready.


Pros and Cons of Low Load vs. High Load Resistance Training

Low-Load / Moderate-Load
​
Pros: Builds muscle, lower injury risk, higher volume without CNS overload, easy form, better mind-muscle connection, aids rehab/joint pain

Cons: Less effective for maximal strength

Form: Encourages strict form, ideal for beginners

Bottom line: Best for volume, muscle engagement, and rehab and learning technique.

High-Load
​
Pros: Builds maximal strength fastest, also builds muscle

Cons: Higher injury risk, more joint stress, CNS fatigue/overuse risk

Form: Risk of poor form, especially for beginners

Bottom line: Best for raw strength, requires careful management.

Matching Load to Your Goal: Strength vs. Hypertrophy

The best approach depends on your specific goal. If your goal is hypertrophy, prioritize higher overall training volume. This is typically best achieved with moderate to low loads, allowing you to accumulate more volume without fatiguing your nervous system as quickly as with heavy weights. The key is performing enough quality work to stimulate growth without burning out.

If your goal is pure strength, heavy load training takes priority. Exercises like heavy squats, deadlifts, and bench presses with heavy loads demand more energy and place greater strain on the body but are essential for building maximal strength.

Strength athletes spend more time lifting heavy, while hypertrophy-focused lifters emphasize moderate to low loads more frequently. But it's not that black and white. Strength athletes also use low to moderate loads, and hypertrophy lifters include heavy sets. The difference lies in the ratio, volume, and overall training context.

For a blend of strength and muscle, vary loads across training phases. Some blocks/ exercises should emphasize heavy lifting for strength; others focus on volume with moderate or lighter weights. Managing fatigue and energy is key to maximizing both.

Summary

Research shows you can build both muscle and strength using any rep range, as long as sets are taken near failure with good form. Muscle growth and strength gains can happen with both low and heavy loads.

However, efficiency and optimization differ:

Muscle growth is more volume-dependent, while strength gains rely more on load. To build muscle, prioritize total training volume and effort across a wide rep range, you don’t need to lift near your 1RM. For strength, focus on heavier sets at higher percentages of your 1RM, though low loads can still increase strength, just at a slower rate.

Many lifters believe that heavy weights are the only path to results, but for those dealing with injuries, limitations, or who cannot train at high intensities, this can be discouraging. Fortunately, evidence shows that muscle growth depends more on training close to muscular failure focusing on exhausting the muscles themselves rather than the nervous system or cardiovascular system—and maintaining sufficient training volume, rather than simply lifting heavy loads.

For those dealing with an injury but still wanting to get stronger, patience and listening to your body should be your primary focus. Start by establishing a baseline with weights and movements that don’t cause pain. Over time, progressively overload by increasing repetitions at the same weight, only moving up in weight when you can do so without discomfort.

With patience, you’ll gradually be able to train closer to your 1RM. Consistent, well-structured training with lighter weights can be just as effective—and often safer—than constantly pushing maximal loads. Ultimately, consistency outperforms intensity, and training smarter leads to better results with fewer setbacks.

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