Eccentric Training Notes

Eccentric Training: Scientific Background and Practical Applications

• Eccentric muscle actions and exercises can enhance strength and athletic performance.
• Eccentric training can lead to larger, stronger muscles with higher power outputs than traditional isotonic training.
• Accentuated eccentric loading (AEL) can provide eccentric overload during multi-joint exercises.

Unique Characteristics of Eccentric Muscle Actions

• Eccentric muscle actions occur when muscle force is less than the external force, causing lengthening.
• During SSC actions, elastic potential energy is stored and released, enhancing force production.
• During deceleration, muscles and tendons act as 'shock absorbers,' dissipating energy as heat.
• Eccentric actions involve increased cross-bridge forces and passive forces from sarcomere elements.
• Muscles can be up to 50% stronger during maximal eccentric exercise versus concentric exercise.
• Energy and activation required are less during eccentric versus concentric or isometric actions for a given force output.
• Eccentric exercise induces lower metabolic and cardiovascular responses than concentric exercise at similar mechanical power output.
• Eccentric actions show reduced muscle activation and discharge rate of motor units compared to concentric actions.
• Eccentric training preferentially recruits higher-threshold motor units.

Benefits of Eccentric Muscle Actions

• Greater work at a given submaximal exercise intensity.
• Tolerance of greater external load during eccentric exercise.
• Potential to stimulate distinct physiological events, increasing fascicle length.
• Fiber shifts to faster myosin heavy-chain isoforms, enhancing force and power production.

Classification of Eccentric Exercise Modalities

• Eccentric training modalities include: isoweight, isokinetic, and isoinertial.
• Isoweight involves constant external load/bodyweight.
• Isoinertial involves constant inertia (e.g., flywheel).
• Isokinetic involves constant velocity (using dynamometry).
• Isopower involves constant power output (using cycle and step ergometry).

Physiological Basis for Eccentric Training

• Acute responses: Myofibrillar disruption, delayed-onset muscle soreness (DOMS), and repeated-bout effect (RBE).
• Microdamage is essential for tissue repair, growth, and protection against future damage.
• Eccentric exercise heightens muscle protein synthesis and anabolic signaling.
• Longitudinal responses: Reduced neural inhibition, increased muscle activation, and shifts towards a faster phenotype.
• Habitual eccentric exercise increases force-producing capacity and muscle cross-sectional area.
• Eccentric exercise stimulates architectural remodeling, increasing fascicle length.

Practical Application of Isoweight Eccentric Training Methods

• Isoweight modalities: tempo training, augmented eccentric training, accentuated eccentric loading (AEL), eccentric-only training.
• Tempo training: Reduces exercise velocity during the eccentric phase.
• Augmented eccentric training: Uses a higher load during the eccentric phase to enhance concentric output.
• Accentuated eccentric loading (AEL): Uses loads >100% 1RM during the eccentric phase.
• Eccentric-only: Emphasizes musculotendinous adaptations to supramaximal eccentric loads.

Important Considerations for Exercise Prescription

• Performance capacity during eccentric muscle actions may not conform to traditional recommendations.
• Alternative methods are needed to prompt greater force output during the eccentric phase.
• Isotonic eccentric exercise intensity is prescribed as a percentage of 1RM.
• Eccentric training volumes should be employed conservatively.
• Traditional 1RM strength tests may overlook task-specificity; eccentric-specific RM assessment may be needed.