Andy Galpin is an exercise and performance scientist and a Professor of Kinesiology. He serves as the Executive Director of the Human Performance Center at Parker University and has held a professorship at California State University, Fullerton. His work focuses on human performance, exercise science, fat loss, and health optimization.
Contracting the glute activates reciprocal inhibition, causing the opposing hip flexor to relax and allowing greater hip range of motion.
"I squeeze my left glute because of reciprocal inhibition. If I squeeze my left glute, it will tell my right hip flexor to turn off. Now I can get more range of motion by squeezing my left glute." (said at 0:05:15)
The concept that contracting an agonist muscle (e.g., gluteus maximus) induces reciprocal inhibition to relax the opposing antagonist (e.g., hip flexors) and improve range of motion is a foundational premise of proprioceptive neuromuscular facilitation (PNF) stretching techniques (specifically the Agonist Contract / CRAC method). While PNF and active stretching techniques do frequently increase joint range of motion, electromyographic (EMG) studies testing the underlying neurophysiological mechanisms have failed to confirm that reciprocal inhibition causes antagonist relaxation during such stretches; studies often observe increased EMG activity (co-contraction) or sensory tolerance changes rather than true reflex-mediated muscle relaxation.
Agility change-of-direction drills with rapid deceleration build tissue tolerance and resilience in the Achilles tendon.
"and we're just going to M drill back and forth. Your quads are going to be on fire, okay? Your feet are going to be working, heart's going to go up, okay, and we're building resilience in your Achilles. Okay, good. Yep, stop, stop, stop. I want you to always stop right here, yeah, and practice deceleration." (said at 0:07:24)
Agility and change-of-direction (COD) drills with rapid deceleration impose high-strain, dynamic stretch-shortening loads on the Achilles tendon. Systematic reviews and meta-analyses show that high-strain mechanical loading (such as high-intensity resistance training and plyometrics) induces favorable tendon adaptations, including increased tendon stiffness, Young's modulus, and cross-sectional area, which together improve tissue tolerance. However, contextual caution is needed: rapid deceleration and change of direction impose extreme peak loads that represent the most frequent mechanism of acute Achilles tendon rupture (accounting for ~40% of in-game ruptures in field athletes), meaning such drills require gradual progression and baseline capacity rather than serving as an entry-level conditioning stimulus.
- supports: Human tendon adaptation in response to mechanical loading: a systematic review and meta-an… (Sports medicine - open 2015)
"The present meta-analysis provides elaborate statistical evidence that tendons are highly responsive to diverse loading regimens. However, the data strongly suggests that loading magnitude in particular plays a key role for tendon adaptation in contrast to muscle contraction type." (abstract, conclusions, passage verified)
pubmedfull study (doi) - supports: Mechanical, Material and Morphological Adaptations of Healthy Lower Limb Tendons to Mechan… (Sports medicine (Auckland, N.Z.) 2022)
"Mechanical loading leads to positive adaptation in lower limb tendon stiffness, modulus and CSA. Studies to date indicate that the main mechanism of increased tendon stiffness due to physical training is increased tendon modulus, and that resistance training performed at high compared to low localised tendon strains is associated with the greatest positive tendon adaptation." (abstract, conclusions, passage verified)
pubmedfull study (doi) - context: Video Analysis of Achilles Tendon Ruptures in the National Football League: Situational Pa… (The American journal of sports medicine 2026)
"Overall, 3 primary injury scenarios accounted for 97% of ATRs: change of direction (40%), overload (30%), and rock back (27%)." (abstract, results, passage verified)
pubmedfull study (doi)
Rhythmic eccentric landing drills build elasticity in the knee, ankle, and lower back tissues safely.
"This is a very safe, injury-free way of building elasticity of your knee, ankle, low back, your grip. And now you're getting rhythm, boom, boom, breathe, arms long, and it's easy, it's smooth." (said at 0:11:03)
Plyometric and eccentric landing drills (involving the stretch-shortening cycle) have been demonstrated to increase tendon stiffness and elastic properties in lower extremity joints (knee and ankle), as shown in systematic reviews and meta-analyses. However, evidence specifically measuring elasticity adaptations in the connective tissues of the lower back from landing drills is limited, and landing drills carry inherent joint loading demands that require appropriate dosage.
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