Strength training: which is more effective – concentric, eccentric or isometric training?

According to sliding filament theory, muscle strength is built between actin and myosin filaments of muscle fibres [1].

What are we talking about?

Muscle action is the term for different biomechanical properties of actin and myosin filaments during activity. These filaments can either move towards each other (concentric), away from each other (eccentric) or not at all (isometric). The terms concentric, eccentric and isometric contractions were introduced to describe these different types of muscle action [2]. In contrast to the terms miometric (Greek for shortening) and pliometric (Greek for lengthening), the terms concentric and eccentric don’t reflect physiological functions. However, they’re still the dominant terms in the literature, so that’s what we’ve used in the rest of this article.
Mechanistically, concentric, eccentric and isometric muscle contractions are differentiated by their ability to build strength. Eccentric methods build between 20 and 50 per cent more strength than concentric ones [3]. Metabolically, eccentric training requires around six times less energy [4]. This means that eccentric contractions are more efficient than concentric contractions.

Concentric versus eccentric

The ability to build more strength during eccentric contractions lead to the hypothesis that this greater mechanical stress could have a bigger impact on hypertrophy or strength [5]. However, it’s important to underline that it’s difficult to link anabolic processes to one of the types of contraction because they have different muscle activations, recruiting, strength capacities and metabolisms.

With the aforementioned discrepancies in mind, Smith and Rutherford [6] used a study design where five men (20.6 ± 0.9 years of age) and five women (20.2 ± 1.3 years of age) trained one leg with concentric contractions of the quadriceps muscles and the other leg with eccentric contractions for 20 weeks. The stress for the eccentric contractions was 35 per cent higher than it was for the concentric contractions. The muscle cross-sectional area was determined using computer tomography. There was a significant increase in muscle mass in both groups. However, there was no significant difference between the legs. Multiple studies which looked at the types of contraction using direct measurements [6–12], lean body mass [13] and the amount [14] of muscle hypertrophy in untrained and trained participants showed no significant differences between them.

The conclusion can therefore be drawn that no clear indication of a superior effect of concentric or eccentric contraction on muscle hypertrophy has been observed [8, 15–21].

Isometric

Multiple studies have looked at isometric training. In 1987, Jones and Rutherford [22] compared the three types of contraction in a study design involving 12 untrained participants (11 men, one woman, 27.5 ± 6 years of age). Six people (five men, one woman) trained one leg with concentric contractions (80 per cent 1-RM, 2-3 seconds per rep) and the other with eccentric contractions (145 per cent 1-RM, 2-3 seconds per rep) on a leg extension machine. Six participants carried out isometric contractions on one leg – building strength without changing muscle length – while the other leg served as the control. All of the contraction types resulted in substantial increases in strength and hypertrophy with no significant differences between them.

Kubo et al. [23] studied the impact of the duration of isometric contractions on the elasticity of human tendons. Eight young men (22.6 ± 2.8 years of age) were also recruited and underwent 12 weeks of training. Muscle volume and strength were measured before and after the study. The researchers used a study design where one leg was assigned a longer contraction protocol and the other was allocated a shorter one. The protocol with a longer stress duration consisted of four sets of four contractions lasting 20 seconds each. The protocol with a shorter stress duration consisted of three sets of 50 reps with each contraction lasting one second. 70 per cent 1-RM was used. The study consisted of 12 weeks, with a training frequency of four days per week. Muscle volume was calculated using MRI. Both protocols resulted in a significant increase in maximum deliberate contraction strength and muscle volume without any significant differences between them.

Conclusion

Hypertrophy triggered by mechanical and metabolic stress can be induced by maximising the fibre recruitment time integral. It's clear that this be achieved via concentric, eccentric and isometric muscle contractions, although activation, recruitment, strength capacity and metabolism are different [24]. The latest literature doesn’t draw any conclusions about the superiority of one muscle action or other. This is why using all contraction types is recommended to increase muscle mass and strength [25].

References

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