Differential Tendon Adaptations In Response To Heavy-load Squat And Light-load Jump Squat Training

Speed, load and range of motion are commonly manipulated exercise programming variables. However, the influence of these variables on tendon adaptations is poorly understood. PURPOSE: To compare the effects of heavy-load squat training to light-load jump squat training on the mechanical and structural properties of the patellar and quadriceps tendon as well as the effects of range of motion used during jump squat training on these adaptations. METHODS: Thirty-six healthy, physically active non-strength trained men underwent ultrasound and dynamometry assessments to determine quadriceps tendon length (Lqt) and stiffness (Kqt), patellar tendon thickness (Tpt), echo-intensity (EIpt) and homogeneity (Hpt). Participants then completed an 8-week intervention of parallel-depth squats (SQ-P, n = 9), parallel-depth jump squats (JS-P, n = 9), volitional-depth jump squats (JS-V, n = 9), or no exercise (C, n = 9) and assessments were then repeated and compared between interventions. RESULTS: No changes were seen in either Lqt (SQ-P: -1.8%, JS-V: 0%, JS-P: -4.4%, C: 0.3%, p > 0.05) or Tpt (SQ-P: 2.9%, JS-V: 2.9%, JS-P: 2.9%, C: -2.7%, p > 0.05). SQ-P reported an increase in Kqt (+54.7%, p < 0.05) while no changes were seen in JS-P, JS-V or C (p > 0.05). Contrastingly, both JS-P and JS-V reported a similar decrease in EIpt (-16.3%, p < 0.05) and an increase in Hpt (JS-P: -11.04%, JS-V: -16.4, p < 0.05) but no changes in either variable were seen in SQ-P or C (p > 0.05). Additionally, direct comparisons between JS-P or JS-V revealed no effect of range of motion on any variable. CONCLUSION: The primary finding of this study was that while knee extensor tendons were affected by both traditional strength (HS-P) and power training (JS-P and JS-V) training the specific adaptations observed differed between these forms of training. Specifically, strength training increased mechanical properties (Kqt) of the tendon independently of changes in tendon structure or composition while power training altered tendon composition (EIpt and Hpt) independently of changes in tendon structure or mechanical properties. A secondary finding was that range of motion used during power training did not affect any observed tendon measurement. In conclusion, the load and speed of training elicited differential tendon adaptions while range of motion had no effect.