Which is better, 80% or 30% of 1 Rep Max for Neuromuscular Adaptation?

Which is better, 80% or 30% of 1 Rep Max for Neuromuscular Adaptation?

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Title: Neuromuscular Adaptations After 2 and 4 Weeks of 80% Versus 30% 1 Repetition Maximum Resistance Training to Failure

Author: Jenkins et al

Journal: American Journal of Strength & Conditioning Research (August 2016, Vol 30, Issue 8, 2174-2185)

Objective: To investigate the hypertrophic, strength, and neuromuscular adaptations to 2 and 4 weeks of resistance training at 80 vs. 30% 1 repetition maximum (1RM) in untrained men.

Background

Classical teaching, supported by the big organizations (NSCA, ACSM), is that 60-85% of 1RM is optimal for muscle hypertrophy. This is however, being challenged by recent experimental evidence. For example, one study showed that 30% vs 90% of 1RM were similar. Subsequently, this has become an area of debate among researchers and weightlifters over optimizing muscle hypertrophy.

The dogma for muscle strength is a little more well established, meaning high load is superior to low load resistance training. For example, 80% of 1RM is superior to 30% of 1RM for strength gains.

What is not well understood is how high-load and low-load influence neuromuscular adaptations. Examples of neuromuscular adaptation from resistance training include neural pathways linked to target muscles become more efficient at transmitting the message; the timing of contractions becomes more coordinated and it can reduce neuromuscular fatigue.

Thus the authors wanted to investigate high- vs low-load effects on neuromuscular adaptations.

Methods

They took 15 untrained men (21 years, weight 84 kg or 184 lb), randomly assigned to either a high-load (n = 7) or low-load (n = 8) resistance training group and completed forearm flexion resistance training to failure 3 times per week for 4 weeks.

Researchers Measured (baseline, week 2, week 4)

  • Forearm flexor muscle thickness (MT)
  • Echo intensity
  • Maximal voluntary isometric contraction (MVIC)
  • 1RM strength,
  • The electromyographic,
  • Mechanomyographic (MMG),
  • Percent voluntary activation (%VA) responses at 10–100% of MVIC

Results

The muscle thickness increase (aka hypertrophy) was similar between both groups.

So let’s talk about changes in strength.

In the 80% 1RM group only,

  • Maximal voluntary isometric contraction increased from week 2 (121.5 ± 19.1 Nm) to week 4 (138.6 ± 22.1 Nm)
  • 1RM increased from baseline (16.7 ± 1.6 kg) to weeks 2 and 4 (19.2 ± 1.9 and 20.5 ± 1.8 kg)

These changes did not occur in the 30% 1RM group.

As for neuromuscular adaptations, there were no significant differences between the groups.

The mechanomyography (MMG) amplitude at 80 and 90% MVIC decreased from baseline to week 4, and percent voluntary action (%VA) increased at 20 and 30% MVIC for both groups and these changes were independent of the training loads.

Conclusions

Muscle hypertrophy was equivalent at the end of 4 weeks of resistance training when using either 30% or 80% of 1RM.

Muscle strength development was superior when training at 80% of 1RM

These strength adaptations were not explained by neuromuscular adaptations because changes were subtle and similar in both groups.

Ultimately, more research is needed to understand high- vs low-load on neuromuscular adaptations

Original Article

Jenkins, N. D., Housh, T. J., & Buckner, S. L. (2016). Neuromuscular Adaptations After 2 and 4 Weeks of 80% Versus 30% 1 Repetition Maximum Resistance Training to Failure. Journal of Strength and Conditioning Research, 30(8), 2174-2185. doi:10.1519/jsc.0000000000001308

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