Research Review: 

Jensen, RL. and Ebben, WP. (2007). Quantifying plyometric exercise intensity via rate of force development, knee joint, and ground reaction forces. Journal of Strength and Conditioning Research, 21(3), 763-767.

Review :

Level of Evidence IB evidence from at least one randomized controlled trial

How This Study is Important: This study quantifying plyometricexercise intensity. Other studies have included intensity based on joint power absorption, time to stabilization, muscle activity, biomechanics.This study provides information about the rates of eccentric force development (E-RFD) in various plyometric exercises. Exercises that required rapid foot adjustment and/or unilateral stances produced higher knee joint reaction forces (K-JRF) K-JRF, although this did not correlate with Peak E-RFD or Peak GRF.  For example, single leg jumps were significantly more “intense” than depth jumps based on K-JRF. However depth jumps showed the highest peak E-RFD.

How the Findings Apply to Practice: This study provides data on the peak ground reaction forces (GRF), rate of eccentric force development (E-RFD) and knee joint reaction forces (K-JRF) for commonly used plyometric exercises. The findings suggest that progressions may need to be modified based on goal and joint “health”,but may be less dependent on GRF

Peak GRF (low-high):Peak E-RFD (low-high):Peak K-JRF (low-high)
Single leg jumpSquat jumpDepth jump (46cm)Pike jumpCountermovement jumpTuck jumpDumbbell squat jumpDepth jump (61cm)Dumbbell squat jump (30%RM)Squat jumpPike jumpSingle leg jumpDepth jump (46cm)Tuck jumpCountermovement jumpDepth jump (61cm)Dumbbell squat jump (30%RM)Countermovement jumpDepth jump (61cm)Depth jump (46cm)Squat JumpSingle leg jumpPike jumpTuck jump

Strengths and Weaknesses: This study had many methodological strengths which include:

  • Exercise randomization and standardized rest periods that reduced bias in the results.
  • Large differences in effects sizes among plyometric exercises were observed in E-RFD, K-JRF and K-JRF/Bodyweight (BW), which reduced the likelihood that these differences occurred by chance.
  • Participants were a wide range of bodyweights (69-96kg)
  • Strengthening the statistical analysis of both GRF/BW and K-JRF/BW.
  • The exercises are commonly used in strength and conditioning to improve performance.
  • How these 3 different measurements (E-RFD, K-JRF and GRF) may co relate with each other.

Weaknesses should be noted prior to clinical integration of the findings:

  • This study has lack statistical power due to the small number of participants and the relatively large variation in plyometric performance among them.
  • Knee joint forces accuracy within this population is unknown.
  • Findings are limited to an athletic population only. It may not be applicable to other populations.

Clinical commentary:

Encourages incorporating progressions into all aspects of an exercise program. This includes (but is not limited to) progressing from isolated activation to integrated activation techniques. Gradully progress from stable to unstable training surfaces in strength training exercises, and from stability/endurance training to max strength/power training. This study’s findings suggest that physiotherapist may need to consider both eccentric rate of force development (E-RFD) and knee joint reaction forces (K-JRF) when determining intensity for plyometric exercise.

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