Isometric contractions, muscle length, and stretching: what the evidence says

Active exercise is the intervention with the highest level of evidence for musculoskeletal pathologies. Isometric contractions performed at longer muscle lengths produce superior adaptations in hypertrophy, strength, and tendon structure. Static stretching increases range of motion but through a predominantly perceptual mechanism, without producing stable structural adaptations. This article collects the data from the literature on these three points.

Active exercise as a first-line intervention

A systematic overview of treatment options for musculoskeletal pain in primary care evaluated the evidence for low back pain, neck pain, shoulder pain, knee pain, and multi-site pain. Therapeutic exercise is supported by moderate to strong evidence for all five pain sites. Passive modalities — ultrasound, TENS, laser, hot and cold packs — show limited evidence and low to moderate results.

Babatunde OO et al. PLoS One. 2017;12(6):e0178621.

A narrative review on chronic musculoskeletal pain confirms that exercise is effective, affordable, and safe, free from the adverse effects of pharmacological treatments and invasive techniques. Significant analgesic effects in osteoarthritis, chronic low back pain, rheumatoid arthritis, and fibromyalgia. Benefits extend beyond pain relief: sleep quality, daily activities, physical function, and emotional state.

Castillo-García M et al. Int J Environ Res Public Health. 2024;21(1):123.

For acute low back pain, a systematic review with meta-analysis of RCTs shows that therapeutic exercise prescribed as an isolated intervention is more effective than standard care in improving short-term disability.

Healthcare. 2025;13(17):2209.

For shoulder pain, exercise-based physiotherapy with resistive loading is recommended as a first-line treatment. Recovery remains limited — between 40% and 50% of patients develop chronic recurrent pain — but resistive exercise consistently improves patient-reported outcomes.

Michener LA et al. JOSPT Open. 2024;2(1):29-48.

The picture is clear. Active exercise is the option with the highest and most consistent level of evidence across musculoskeletal pathologies.

Isometric contractions at longer muscle lengths

Muscular and tendon adaptations

A systematic review of 26 studies analysed the effects of isometric training on muscle and tendon, examining three variables: muscle length, intensity, and contraction type.

Isometric contractions performed at longer muscle lengths produce significantly greater hypertrophy than the same contractions at shorter lengths. They produce greater transferability to dynamic performance. For tendon adaptations, high-intensity contractions are required — at least 70% of maximal voluntary contraction.

Oranchuk DJ et al. Scand J Med Sci Sports. 2019;29(4):484-503.

Muscle length during isometric contraction is the determining variable for the magnitude of adaptations.

Analgesic effects in tendinopathies

A randomised crossover study on athletes with patellar tendinopathy compared isometric and isotonic contractions. Isometric contractions reduced pain from 7.0 to 0.17 on a 0–10 scale — a 6.8-point reduction. Isotonic contractions: 2.6 points. The analgesic effect of isometric contractions was maintained for at least 45 minutes. Simultaneously, isometric contractions increased maximal voluntary contraction strength by 18.7% and released cortical inhibition.

Rio E et al. Br J Sports Med. 2015;49(19):1277-83.

A systematic review with meta-analysis on various tendinopathies (patellar, rotator cuff, lateral elbow, Achilles, gluteal) confirms that isometric contractions reduce pain and improve functional disability. When time under tension is equalised, isometric and isotonic contractions produce comparable results — isometric contractions can be used both for acute pain relief and for progressive tendon loading.

Clifford C et al. BMJ Open Sport Exerc Med. 2020;6(1):e000760.

Effects in knee osteoarthritis

A meta-analysis of 9 studies and 688 participants shows significant pain reductions, improvements in physical function, and increased muscular strength compared to controls.

J Musculoskelet Neuronal Interact. 2024.

Muscle activation

During resistive isometric exercise, muscle activity is systematically higher at longer lengths than at shorter lengths — even when forces are equalised. Electromyographic amplitudes and voluntary activation are significantly higher. Force production at longer lengths requires greater motor unit recruitment or higher firing rates.

Maximal isometric contractions produce significantly greater muscle activation than maximal eccentric and concentric contractions.

McMahon G. Exp Physiol. 2025.

Static stretching: what the data say

Resistance training improves range of motion as much as stretching

A meta-analysis of 55 studies shows that resistance training with external loads significantly increases range of motion. The central finding: no significant differences were found between resistance training and stretching in improving range of motion. Stretching before or after resistance training may not be necessary to improve flexibility.

Alizadeh S et al. Sports Med. 2023;53(3):707-722.

A previous meta-analysis of 11 studies and 452 participants confirms: no significant difference between strength training and stretching on range of motion.

Afonso J et al. Healthcare. 2021;9(4):427.

A third meta-analysis from 2025, on 36 studies and 1,469 participants, confirms that resistance training significantly improves joint flexibility. High-intensity protocols produce greater effects.

Favro F et al. J Strength Cond Res. 2025;39(3):386-397.

Static stretching and performance

Static stretching produces a performance reduction of approximately 3.7%, with greater deficits (4.6%) when duration exceeds 60 seconds. It reduces muscle-tendon unit stiffness and motor unit firing rate. The central nervous system cannot activate muscles with the same speed and intensity after prolonged static stretching.

Behm DG et al. Appl Physiol Nutr Metab. 2016;41(1):1-11.

Static stretching and muscle-tendon stiffness

Acute static stretching reduces muscle-tendon stiffness. Long-term effects on stiffness remain uncertain.

Takeuchi K et al. J Sports Sci Med. 2023;22(3):465-475.

What static stretching produces and what it does not

Static stretching increases range of motion. The mechanism is predominantly perceptual: reviews indicate that improvement occurs through increased stretch tolerance, not through stable modification of the mechanical properties of the tissue.

Static stretching does not produce increased muscle hypertrophy. It does not produce structural tendon adaptations. It does not produce strength gains. It does not produce the neuromuscular activation necessary for long-term adaptations.

Resistance training improves range of motion as much as stretching and simultaneously produces hypertrophy, tendon adaptations, strength, and neuromuscular function.

Clinical application

Isometric contractions performed at maximum physiological lengthening combine three elements that the literature identifies as determining factors:

Active exercise — the intervention with the highest level of evidence for musculoskeletal pathologies.

Longer muscle length — the variable that produces superior adaptations in hypertrophy, strength, tendon structure, and transferability.

Loading of connective tissue components — muscular connective tissue exhibits plastic behaviour: subjected to sufficient force for sufficient time it deforms, and the deformation can become stable. This is the basis for reducing Resistant Force.

This clinical toolset derives from the original work of Françoise Mézières and constitutes the therapeutic foundation of the biomechanical model taught by AIFIMM — Institute of Applied Musculoskeletal Biomechanics.

This topic is part of the online course Systemic and Segmental MSK Biomechanics.

References

[1] Babatunde OO, Jordan JL, Van der Windt DA, Hill JC, Foster NE, Protheroe J. Effective treatment options for musculoskeletal pain in primary care: A systematic overview of current evidence. PLoS One. 2017;12(6):e0178621. [2] Castillo-García M, Navarro-Ledesma S, León-Morillas F, Tapia-Haro RM, Gómez-Urquiza JL, Sánchez-Cuesta FJ. The Role of Physical Exercise in Chronic Musculoskeletal Pain: Best Medicine—A Narrative Review. Int J Environ Res Public Health. 2024;21(1):123. [3] Healthcare. Isolated Exercise Interventions for Acute Low Back Pain: Systematic Review and Meta-Analysis of Randomized Controlled Trials. Healthcare. 2025;13(17):2209. [4] Michener LA et al. Adding Manual Therapy to an Exercise Program Improves Long-Term Patient Outcomes Over Exercise Alone in Patients With Subacromial Shoulder Pain: A Randomized Clinical Trial. JOSPT Open. 2024;2(1):29-48. [5] Oranchuk DJ, Storey AG, Nelson AR, Cronin JB. Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review. Scand J Med Sci Sports. 2019;29(4):484-503. [6] Rio E, Kidgell D, Purdam C, Gaida J, Moseley GL, Pearce AJ, Cook J. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. Br J Sports Med. 2015;49(19):1277-83. [7] Clifford C, Challoumas D, Paul L, Syme G, Millar NL. Effectiveness of isometric exercise in the management of tendinopathy: a systematic review and meta-analysis of randomised trials. BMJ Open Sport Exerc Med. 2020;6(1):e000760. [8] Isometric exercise for knee osteoarthritis: A systematic review and meta-analysis. J Musculoskelet Neuronal Interact. 2024. [9] McMahon G. Isometric training at longer muscle-tendon complex lengths: A potential countermeasure to impaired neuro-muscle-tendon function during space travel. Exp Physiol. 2025. [10] Alizadeh S, Daneshjoo A, Zahiri A, Anvar SH, Goudini R, Hicks JP, Konrad A, Behm DG. Resistance Training Induces Improvements in Range of Motion: A Systematic Review and Meta-Analysis. Sports Med. 2023;53(3):707-722. [11] Afonso J, Ramirez-Campillo R, Moscão J, Rocha T, Zacca R, Martins A, et al. Strength Training versus Stretching for Improving Range of Motion: A Systematic Review and Meta-Analysis. Healthcare. 2021;9(4):427. [12] Favro F, Roma E, Gobbo S, Bullo V, Di Blasio A, Cugusi L, Bergamin M. The Influence of Resistance Training on Joint Flexibility in Healthy Adults: A Systematic Review, Meta-analysis, and Meta-regression. J Strength Cond Res. 2025;39(3):386-397. [13] Behm DG, Blazevich AJ, Kay AD, McHugh M. Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: a systematic review. Appl Physiol Nutr Metab. 2016;41(1):1-11. [14] Takeuchi K, Sato M, Fujita T, Murakami T. Acute and Long-Term Effects of Static Stretching on Muscle-Tendon Unit Stiffness: A Systematic Review and Meta-Analysis. J Sports Sci Med. 2023;22(3):465-475.