Publications
Relationship between rectus femoris stiffness, muscle activity, and force production during graded isometric contractions measured by handheld myotonometry
Authors: Serkan Tas 1, Dilek Hande Esen 2, Veysel Alcan 3, Yusuf Muratoglu 4
Affiliations:
- Faculty of Health Sciences, Department of Physical Therapy and Rehabilitation, Toros University, Mersin, Turkey
- Vocational School of Health Services, Department of Therapy and Rehabilitation, Toros University, Mersin, Turkey
- Faculty of Engineering, Department of Electrical and Electronic Engineering, Tarsus University, Mersin, Turkey
- Vocational School, Department of Electronics and Automation, Toros University, Mersin, Turkey
Journal: Journal of Sports Sciences - October 2026 (DOI: 10.1080/02640414.2026.2750627)
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Field & Applications:
- Medical
- Sport
- Neuromuscular response
- Muscle development / Performance
- The associations between muscle stiffness, EMG activity, and strength production suggest that myotonometer-derived stiffness can serve as a potential complementary predictor of muscle activation and strength, particularly when reliable EMG recordings are difficult to obtain, such as in individuals with pain, neurological disorders, or postoperative limitations.
Surface electromyography (sEMG) is widely used to assess muscle activation; however, practical limitations may restrict its routine clinical use. Handheld myotonometry, which may provide complementary information on the mechanical behavior of active muscles, was used to examine the association between rectus femoris (RF) muscle stiffness, sEMG amplitude, and isometric knee extension force across graded contraction intensities.
Fifteen healthy adults performed isometric knee extensions at 0%, 10%, 20%, 30%, 50%, 70%, and 100% of their maximum voluntary contraction (MVC). RF stiffness, sEMG root mean square amplitude, and knee extension force were recorded at each contraction level.
RF stiffness increased with contraction intensity and showed a strong positive association with the sEMG amplitude (R2 = 0.706). Stiffness was also associated with the knee extension force (R2 = 0.561). Although the EMG amplitude increased with contraction intensity, no significant difference was observed between 70% and 100% MVC, whereas stiffness continued to differentiate between these higher contraction levels.
RF muscle stiffness was strongly associated with sEMG amplitude and knee extension force during graded-isometric contractions. These findings suggest that handheld myotonometry may provide a practical complementary measure of the muscle mechanical response associated with the activation level under standardized conditions.
Keywords: stiffness, MyotonPRO, surface EMG activity, isometric contraction, quadriceps femoris
RF muscle stiffness measured by handheld myotonometry was strongly associated with sEMG amplitude and isometric knee extension force during graded isometric contraction, although sEMG amplitude remained the stronger predictor of force. Handheld myotonometry may therefore provide a practical complementary measure of muscle mechanical response associated with activation level under standardized testing condition, particularly when EMG recording is not feasible.