Calcaneal tendon stiffness is not associated with dynamic time-dependent contractile output

Area of Science:

• Biomechanics
• Musculoskeletal Physiology
• Sports Science

Background:

• Rapid muscular torque and velocity generation are crucial for athletic performance and daily activities.
• Tendon stiffness is a key factor in transmitting musculoskeletal forces.
• Previous research shows weak-to-moderate links between tendon stiffness and rate of torque development (RTD), primarily in isometric contractions.

Purpose of the Study:

• To examine the influence of calcaneal tendon stiffness on dynamic RTD and rate of velocity development (RVD) in plantar flexor muscles.
• To determine if correlations between tendon stiffness and torque/velocity development differ between isometric and dynamic contractions.

Main Methods:

• Ultrasound imaging was used to measure tendon morphological characteristics and estimate Young's elastic modulus (YM).
• Participants performed maximal voluntary and electrically evoked isometric and isotonic plantar flexion contractions.
• RTD and RVD were assessed during dynamic contractions under varying loads (10% and 40% MVC).

Main Results:

• Young's elastic modulus (YM) correlated with evoked isometric RTD (RTD0–50ms: r=0.54, p=0.02; RTD0–200ms: r=0.62, p=0.01).
• No significant correlations were found between YM and dynamic RTD or RVD in either voluntary or evoked contractions.
• These findings indicate calcaneal tendon stiffness is important for isometric, but not dynamic, rapid torque production.

Conclusions:

• Calcaneal tendon stiffness is a significant determinant of rapid torque development during isometric contractions.
• The relationship between tendon stiffness and rapid torque/velocity development is less pronounced during dynamic, isotonic contractions.
• Factors beyond tendon stiffness, such as muscle contractile properties, likely play a more critical role in dynamic performance.