Eccentric Training: How the Negative Phase Builds Muscle and Restores Tendons

What is the eccentric mode?

Muscles work in two primary modes: concentric (shortening against resistance) and eccentric (lengthening under load, yielding to resistance). Everyday training examples include lowering the bar to the chest in the bench press, the descent phase of the squat, the slow return to starting position in the Nordic hamstring curl, and lowering the heel during calf exercises.

The key property of eccentric work: at the same physiological cross-sectional area, a muscle can produce greater force eccentrically than concentrically. This means mechanical tension at the sarcomere level is higher — which has direct consequences for adaptation.

Although the negative phase is present in every repetition, deliberately emphasising it — slowing down, adding extra load, using isolated eccentric exercises — alters the character of adaptation. This is what current meta-analyses are investigating.

Why does eccentric training produce unique adaptations?

The mechanism absent from concentric work to the same degree is loading under stretch at long muscle length. When a muscle is stretched under load rather than simply shortening, sarcomeres experience tension in an unfavourable position on the force-length curve. This unstable state activates specific signalling pathways that lead to the addition of new sarcomeres not in parallel (which increases cross-sectional area) but in series. The result: muscle fascicles become longer.

Bizet et al. (Journal of Applied Physiology, 2025) tested this mechanism directly. 33 young adults completed an 8-week eccentric training programme divided into two groups: eccentric at long muscle length and eccentric at short muscle length. Result: in the long-length group, fascicle length of the medial head of the gastrocnemius increased by 8.5%. In the short-length group, no significant changes were found. This is direct evidence that what matters is not eccentric training per se, but eccentric training in the stretched position.

A second unique effect is the acceleration of muscle protein synthesis following eccentric damage. Jameson et al. (American Journal of Physiology, 2022) conducted a study in 21 men: in the eccentric damage group, the rate of myofibrillar protein synthesis was 2.57% per day versus 1.89% per day in the control group during the first 48 hours — an increase of 48%. This suggests that the damaging stimulus initiates an intense remodelling process that, given adequate recovery, is converted into hypertrophy.

Hypertrophy: comparable to concentric, but with nuances

Da Silva et al. published in the Journal of Strength and Conditioning Research (2024) a meta-analysis of 26 RCTs with 682 participants comparing eccentric and concentric loading for hypertrophy at equated volume.

Overall result: no significant difference (ES=0.285; 95% CI: -0.131–0.701; p=0.179). Eccentric training is not more magical than concentric when all else is equal. However, subgroup analyses revealed important nuances:

• For upper-limb muscles, eccentric training showed a significant advantage: ES=1.44 (95% CI: 0.179–2.692; p=0.025) — a large effect by Cohen's classification.
• For muscle thickness (ultrasound measurement), eccentric training had a statistically significant advantage (p=0.0352).
• Without volume equating, the comparison loses meaning: simply lowering the weight more slowly does not produce a magical effect — sufficient load is required.

Practical conclusion: eccentric training is not a replacement for concentric, but a complement with targeted advantages, especially for the upper body and fascicle lengthening.

Nordic hamstring curl: muscle and injury prevention

The Nordic hamstring curl (lowering the torso forward from a position with the ankles fixed) is one of the few exercises that loads the biceps femoris eccentrically at long muscle length. This is precisely why it has become the subject of large-scale research in football, where hamstring injuries rank first in frequency and duration of forced absence.

Cholp and Zemkova (Frontiers in Physiology, 2025) conducted a systematic review and meta-analysis of 11 studies in football players, comparing high and low volumes of the Nordic hamstring curl. Results for the high-volume group:

• Eccentric strength of the biceps femoris: g=0.77 (p<0.001) — large effect
• Fascicle length: g=0.43 (p<0.001) — moderate effect
• Muscle thickness: g=0.48 (p<0.001) — moderate effect

The preventive effect is confirmed by separate meta-analyses: programmes that include the Nordic hamstring curl reduce hamstring injury incidence by approximately 51% (IRR approximately 0.49; 95% CI: 0.291–0.827).

The protective mechanism is well understood: longer fascicles contain more sarcomeres in series, which shifts the peak force on the force-length curve towards greater stretch. During sprinting and sharp accelerations — when the biceps femoris is loaded precisely in the stretched position — an athlete with longer fascicles is less likely to exceed the optimal working range of the muscle.

Achilles tendinopathy

Eccentric loading has long been applied in tendon rehabilitation, but the quality of the evidence base was low until recently. Yuan et al. published in BMC Musculoskeletal Disorders (2026) a meta-analysis of 21 RCTs with 994 participants, comparing eccentric exercise with physiotherapy modalities — ultrasound and laser therapy.

Results in favour of eccentric training:

• Pain on the visual analogue scale: SMD=-0.54 (95% CI: -0.92 to -0.17) — significant reduction
• Tendon function on the VISA-A scale: SMD=-0.54 (95% CI: -0.80 to -0.28) — significant improvement
• Tendon thickness on ultrasound: SMD=0.41 (95% CI: 0.12–0.70; I²=0%) — reduction in pathological thickening

Zero heterogeneity (I²=0%) for tendon thickness is a rare finding in clinical meta-analyses, indicating high reproducibility of the effect across studies.

The classic Alfredson protocol, on which most included studies are based: heel drops with added load — 3 sets of 15 repetitions twice daily, with progressive load increase. Key condition: the exercise is performed with moderate pain (not zero) — this is considered acceptable and functionally necessary to stimulate tendon adaptation.