Professional Baseball Strength & Conditioning


Plyometric Training and The Vertimax

By Mike Lidge MS, RSCC

Research Behind Plyometrics. Plyometrics are used to improve lower body power and increase explosiveness by training the muscle to do more work in a shorter period of time1. This is achieved by activating the stretch-shortening cycle (SSC), which occurs when an active muscle(s) switches from a rapid eccentric muscle action (deceleration) to a rapid concentric muscle action (acceleration)2.  The eccentric movement creates a stretch reflex producing a more forceful concentric muscle action than could otherwise be generated2.  Plyometric exercises that exploit the SSC have been shown to enhance the performance of the concentric phase of the movement and increase power3. It can be said that true plyometric training requires a rapid pre-stretch through eccentric contraction of the muscle followed by immediate max effort concentric contraction of the muscle, which can be accomplished in various forms of jumps4.

Incorporating Reactive Strength Index (RSI). The vertical jump has long been the “gold standard” in measuring relative lower body power through vertical displacement. Reactive strength index (RSI) is a relatively new term of measurement used to evaluate an athlete’s SSC power endurance (or muscle elasticity) when performing elastic based plyometrics (plyos). Compared to conventional based plyos (box jumps, depth jumps), elastic based plyos (continuous hurdle jumps, jump rope double unders, bounding) are performed continuously at max effort. Elastic based plyos are considered to be at the extreme high end of the force velocity curve and require maximal SSC output and impulse to allow an athlete to get off the ground as fast as possible while at the same time achieving as much displacement as possible. When measuring reactive strength index using vertical displacement, a jump mat can be used to calculate the RSI of each jump from the time in the air and touch time on the mat. As with any plyometric exercise, it is still imperative to cue the athlete to use “triple extension” of the hips, knees and ankles to ensure that the results aren’t skewed when using the jump mat.

What We Know About the Vertimax. While often thought of as solely a vertical height trainer, the Vertimax (Vmax) can also be used to train an athlete to move explosively through all three planes of motion (sagittal, frontal, and transverse planes). The Vmax uses consistent pulley tension, which differs from a typical elastic band or bungee that changes in resistance as the band is stretched or shortened. Cable attachments are located at the front of the platform for horizontal displacement exercises, and on top of the platform for vertical displacement exercises. The athlete is attached to the device via a waist belt attached to bands that create force vectors that require the athlete to move efficiently and under control. Research comparing the effectiveness of the Vmax to traditional plyo exercise methods performed in the sagittal plane (vertical displacement) supports the use of the Vmax. McClenton, et. al., for example, found that subjects who trained on the Vmax for six weeks made improvements in vertical jump similar to those who performed depth jump training for six week5.

Similar results were observed by Rhea, et. al., who compared a group of college athletes that trained using the Vmax and strength training to a group that trained using traditional plyometric exercises and strength training. After 12-weeks, the group that trained using both the Vmax and strength training displayed a significantly higher level of power output than the group that performed traditional plyos plus strength training6.

Rate of Force Development and Post Activation Potentiation. Research data suggest that combining heavy resistance training with high-speed exercises may be the optimal technique for eliciting neuromuscular adaptations that support both the stretch reflex and rate of force development (RFD)7.  Post activation potentiation (PAP) is the increase in muscle force and RFD that occurs as a result of previous activation of the muscle, as well as the force and power of evoked in high velocity shortening contractions8. In other words, excitation of the central nervous system produces an increase in contractile function due to a heavy load conditioning stimulus9. PAP is often used by “super setting” a plyometric exercise immediately after a heavy compound movement exercise such as a squat, deadlift of lunge. No research was found comparing increases in RFD with PAP training when using the Vmax versus conventional plyos.

Summary. The Vmax can be a useful tool in providing variability with plyo training. The Vmax could potentially be more effective than conventional plyos in increasing RFD when coupled with strength training. When compared to the box jump (concentric based) and depth jump (eccentric based), the Vmax combines the benefits of both by using consistent tension loaded at the hips throughout the movement. This increases the importance of the athlete to be able to display proper landing mechanics and body control through near maximal effort plyometric movements. Program design and implementation should take into consideration the increased stimulus the athlete faces through both concentric and eccentric muscle contractions when using the Vmax.

For more information on VertiMax please visit


  1. Holcomb, WR, et. al. The effectiveness of a modified plyometric program on power and the vertical jump. J Strength Cond Res 10: 89–92, 1996.

  2. Potteiger, JA, et. al. Muscle power and fiber characteristics following 8 weeks of plyometric training. J Strength Cond Res 13: 275–279, 1999.

  3. Gehri, DJ, et. al. A comparison of plyometric training techniques for improving vertical jump ability and energy production. J Strength Cond Res 12: 85–89, 1998.

  4. Lachance, PF. Plyometric exercises. Strength Cond 8: 16–23, 1995.

  5. Rhea, MR, et. al., An examination of training on the VertiMax resisted jumping device for improvements in lower body power in highly trained college athletes. J Strength Cond Res 22:735-740, 2008.

  6. Harris, GR., et. al. Short-term performance effects of high power, high force or combined weight-training methods. J Strength Cond Res 14:14-20, 2000.



LAKEYSHA S. MCCLENTON, LEE E. BROWN, JARED W. COBURN, AND ROBERT D. KERMcClenton, L, Brown, L., Coburn, JW., Kersey RD. The effect of short-term VertiMax vs. depth jump training on vertical jump performance. J Strength Cond Res. 2008; Mar;22(2):321-5.

  1. Mitchell CJ and DG Sale. Enhancement of jump performance after a 5-RM squat is associated with postactivation potentiation. Eur J Appl Physiol. 2011.

  2. Judge LW. The application of postactivation potentiation to the track and field thrower. Strength Cond J 31:34–36, 2009.


Mike Lidge, MS, RSCC is a Minor League Strength and Conditioning Coach for the Philadelphia Phillies.

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