Squat Jump Test (SJ)

Evaluate pure explosive leg power without stretch-shortening cycle contribution.

Squat Jump Test (SJ)

Test Objective

To evaluate the explosive power of the lower limbs in isolation, without the influence of momentum or stretch reflex (no preliminary countermovement).

Required Equipment

  • Contact platform (jump mat) or jump timer (optical or inertial).
  • OR a measuring tape (if the jump height is measured against a wall).
  • A stable and non-slip surface.
  • An assistant or a sensor to measure the jump height.

Test Protocol

  • The subject starts in a squatting position (approximately 90° at the knees), with feet flat on the floor, trunk straight, and hands placed on the hips.
  • They must maintain this static position for 1 to 2 seconds (strictly no bouncing or dipping).
  • On the signal, they perform a maximal vertical jump, without any arm swing (hands must remain on the hips at all times).
  • The jump height is measured either by:
    • Flight time (using a contact platform or sensor).
    • Height reached on a graduated wall (a less precise method).

Evaluation

  • Perform 2 to 3 trials and record the best jump (expressed in cm).
  • Mechanical power can be calculated using specific equations (such as the Bosco equation).
  • The test allows for the evaluation of explosive strength without the contribution of the stretch-shortening cycle (SSC), unlike the CMJ (Countermovement Jump).

Interpretation of Results

  • Low jump height: Indicates a deficit in explosive power or poor jumping technique.
  • Comparing the SJ with the CMJ (Countermovement Jump) allows coaches to evaluate the athlete's utilization of the stretch-shortening cycle (SSC):
    • If CMJ >> SJ (CMJ is significantly greater than SJ): Indicates good utilization of the SSC.
    • If CMJ ≈ SJ (CMJ is approximately equal to SJ): Indicates a deficit in explosiveness or neuromuscular coordination.

Recommendations

  • Thoroughly warm up the leg muscles before starting the test.
  • Strictly monitor adherence to the initial static position (ensure there is no pre-jump downward dip or countermovement).
  • Perform the test on a flat, safe, and non-slip surface.

 

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