Neuromuscular Fatigue: Light Weights vs Heavy Weights |

This study explored whether lighter weights for many repetitions or heavier weights for fewer repetitions create more neuromuscular fatigue when total work is matched. Five trained men completed six bench-press protocols using either 50 percent or 85 percent of their one-repetition maximum. The researchers measured bar speed, jump performance, lactate levels, and subjective fatigue. The results showed that lighter weights taken to failure caused the greatest neuromuscular and perceptual fatigue, including more soreness and slower recovery. Heavier weights created less overall fatigue, especially when using strategies like cluster sets or stopping short of failure. In short, heavier lifting allowed athletes to feel and perform better the next day.

Key Takeaways of Neuromuscular Fatigue Article

Light weights cause greater neuromuscular fatigue when taken to failure than heavier weights.
Heavier loads (around 85% of your max) create less neuromuscular and perceptual fatigue while promoting similar muscle growth.
Training to failure isn’t always necessary — proper intensity and rest days can help reduce fatigue and improve long-term results.

Introduction

It’s well documented that muscle growth can be accomplished using both higher reps with lighter weights and lower reps with heavier loads. This debate — often framed as “high reps vs low reps” — has dominated strength training discussions for years.

However, a 2024 study by Varela-Olalla and colleagues published in the Journal of Functional Morphology and Kinesiology revealed a surprising finding: lighter weights performed to failure actually induce more neuromuscular fatigue than lifting heavy weights with fewer repetitions.¹

This study—conducted on five trained men aged around 21 years performing bench press at 50% and 85% of their one-repetition max—suggests that high-rep, low-load training can be more fatiguing for both the muscles and nervous system.

Review of the Literature: High Reps vs Low Reps and Neuromuscular Fatigue

The comparison of high reps vs low reps has sparked significant research on how training intensity influences neuromuscular fatigue. Studies show that training to failure with lighter weights increases both metabolic and perceptual fatigue, while heavier weights performed with fewer reps result in less overall stress on the nervous system.

For example, Jackson et al. (2007) demonstrated that high-repetition, low-intensity workouts generated greater muscle fatigue and lactate buildup.² Similarly, Raastad et al. (2003) found that high-volume training caused more muscle damage and hormonal disturbances than shorter, high-intensity sessions.³

Salvador et al. (2023) added that lighter, high-repetition training primarily activates slow-twitch muscle fibers, which sustain contractions longer but accumulate more fatigue over time.¹

Together, these findings suggest that the fatigue cost of high-rep training outweighs the benefits when recovery and performance are considered. This reinforces the importance of rest days and managing training intensity to balance muscle growth and recovery.

Study Overview: Testing Training to Failure and Fatigue

In the 2024 study by Varela-Olalla et al., five trained men performed six different bench press routines, alternating between light weights (50% of one-rep max) and heavy weights (85% of one-rep max).

Each participant completed sessions that included:

Traditional sets to failure, testing how training to failure affects fatigue.
Half-volume sets, stopping at half the usual reps.
Cluster sets, including short rest periods within each set to manage neuromuscular fatigue.

Researchers measured:

Movement velocity (bar speed — a sign of neuromuscular efficiency).
Lactate levels (metabolic stress).
Perceived effort and discomfort (mental fatigue).
Muscle soreness and fatigue after 24 and 48 hours to test the importance of rest days.

Results: Heavier Weights Caused Less Neuromuscular Fatigue

Surprisingly, light weight, high-rep training to failure created the most pronounced neuromuscular fatigue. Participants lost more bar speed, showed higher lactate buildup, and reported greater discomfort immediately after these sessions.

On the other hand, heavy weight, low-rep training produced significantly lower neuromuscular and perceptual fatigue — even though the total work was matched.

Key results included:

Lower movement velocity after light-load training (indicating impaired neuromuscular performance).
Higher lactate levels and muscle soreness 24–48 hours later.
Perceived effort (RPE) scores that were much higher during light-load sets to failure.
Simply put, lifting lighter weights to failure is more exhausting—neurologically and metabolically—than performing heavier sets with fewer reps.

What Causes More Neuromuscular Fatigue in High-Repetition Training?

So, why does high-rep, light weight training lead to greater neuromuscular fatigue? There are several key mechanisms:

Time under tension – Light loads keep muscles contracting longer (up to 60 seconds per set), increasing stress and metabolic by-products like lactate.
Metabolic overload – Accumulation of metabolites interferes with muscle contraction, leading to greater fatigue and slower recovery.
Neural drive – Heavy training activates powerful fast-twitch fibers for shorter durations, allowing quicker neural recovery.
Perceptual fatigue – Long, high-rep sets feel mentally tougher, increasing discomfort and reducing training motivation.

The findings challenge the assumption that “more is always better.” While training to failure with high reps may stimulate growth, it also drains energy reserves and increases recovery demands—highlighting the importance of rest days for restoring neuromuscular function.

Practical Applications: How to Train Smart and Manage Neuromuscular Fatigue

Here’s how to apply these findings to your training program:

Choose the right load. Training in the 70–85% range of your one-rep max (about 8–10 reps) balances hypertrophy and performance while minimizing neuromuscular fatigue.
Avoid frequent training to failure. Reserve it for occasional sessions or deload weeks to prevent overtraining.
Use cluster sets. Taking 20–30 second breaks within a set can reduce fatigue and maintain movement quality.
Prioritize rest days. Recovery allows your nervous system and muscles to adapt—skipping rest is one of the main causes of chronic neuromuscular fatigue.
Monitor bar speed and effort. Slower reps often signal fatigue buildup—an early warning that you might need more rest or reduced volume.

Remember: strength and muscle growth aren’t just built in the gym—they’re built during rest days when recovery and adaptation occur.

The Real Lesson Behind Neuromuscular Fatigue

The evidence is clear — heavy training may cause less neuromuscular fatigue than high-repetition light-load workouts, even when both build muscle effectively.

Light weight training to failure drives fatigue higher, increasing recovery time and discomfort, while moderate-to-heavy loads with controlled effort allow for consistent, sustainable progress.

By balancing training intensity with the importance of rest days, athletes can grow stronger, recover faster, and prevent long-term fatigue that can stall progress.

In short: when it comes to high reps vs low reps, heavier might just mean smarter.

Frequently Asked Questions (FAQs)

What is neuromuscular fatigue and why does it matter?

Neuromuscular fatigue refers to a decline in muscle performance caused by stress on both the muscles and the nervous system. It matters because excessive fatigue reduces power output, recovery capacity, and training efficiency.

Is training to failure necessary for muscle growth?

No, research shows that training to failure increases neuromuscular fatigue and can slow recovery. Stopping one or two reps short of failure can still promote growth while protecting the nervous system.

Which is better for building muscle — high reps or low reps?

Both can build muscle, but low reps with heavier loads tend to cause less neuromuscular fatigue and promote strength, while high reps increase fatigue and soreness. A mix of both is ideal depending on your goals.

How many rest days should I take per week?

Most people benefit from 1–2 rest days per week to prevent accumulated neuromuscular fatigue. Advanced lifters may use active recovery instead of full rest depending on training intensity.

Does lifting heavy weights cause more fatigue than light weights?

Not necessarily. The study by Varela-Olalla et al. (2024) showed that light weights to failure caused more fatigue than heavy weights with fewer reps, even though both led to similar muscle activation.

References

1 Salvador, P. C. d. N., Nascimento, E. M. F., Antunes, D., Guglielmo, L. G. A. & Denadai, B. S. Energy Metabolism and Muscle Activation Heterogeneity Explain V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ Slow Component and Muscle Fatigue of Cycling at Different Intensities. Experimental Physiology 108, 503-517 (2023). https://doi.org/10.1113/ep090444

2 Jackson, N. P., Hickey, M. S. & Reiser, R. F. High Resistance&thinsp;/&Amp;thinsp;Low Repetition vs. Low Resistance&thinsp;/&Amp;thinsp;High Repetition Training: Effects on Performance of Trained Cyclists. The Journal of Strength and Conditioning Research 21, 289 (2007). https://doi.org/10.1519/r-18465.1

3 Raastad, T., Glomsheller, T., Bjøro, T. & Hallén, J. Recovery of Skeletal Muscle Contractility and Hormonal Responses to Strength Exercise After Two Weeks of High‐volume Strength Training. Scandinavian Journal of Medicine and Science in Sports 13, 159-168 (2003). https://doi.org/10.1034/j.1600-0838.2003.00297.x