Physical capacity and mechanical efficiency are both critical in producing the highest possible velocity for an individual pitcher. I’ve covered the importance of lead leg block previously so in this article I’m going to focus on a specific piece of physical capacity necessary for an efficient lead leg, reactive strength.

What is Reactive Strength?

Reactive strength represents the function of the fast stretch shortening cycle (SSC). The SSC is utilized when a muscle-tendon unit is stretched immediately before a contraction. This results in the enhancement of that performance due to the myotatic or stretch reflex, the storage and utilization of elastic energy, and increased motor unit recruitment (Flanagan, 2009). In order to take advantage of the SSC the coupling time between eccentric and concentric actions must be short. This means if there is a significant delay between the eccentric action and the following concentric action, the enhancement is unlikely to take place. The SSC can be divided into fast and slow based on contraction or ground contact times, with the fast SSC taking <250ms and the slow SSC using >250ms.

What Does an Effective Lead Leg Block Achieve?

The lead leg block is the transition from linear to rotational, and transfers energy from the lower body to the trunk. Linear energy is built up by the lower body, while rotational energy is stored in both the upper and lower body. Heading into foot strike, the lower body becomes rotational, but in order for the upper body to follow suit at the highest possible level there must be a stable base for rotation to occur around. In order for energy to be successfully transferred to the trunk, forward movement must be quickly stopped and redirected against the direction of the throw (Guido and Werner, 2012). The faster the transition from stopping to redirecting, the more effectively energy is transferred.  Research has shown that the lead leg block of a high velocity delivery has greater knee extension, greater knee extension angular velocity, produces higher ground reaction force (GRF), and redirects force against the direction of the throw (Guido and Werner, 2012) (van Trig et al., 2018). This must happen extremely fast in order for the linear force to be effectively transferred. If a pitcher is unable to stop and redirect this force, or if he does so too slowly, throwing velocity will not be maximized.

Why Does Reactive Strength Matter?

Explosive movements that use a high level of linear momentum which must then be abruptly stopped and transferred in a different direction rely heavily on reactive strength. Think about a basketball player running in for a dunk-they build up a lot of speed and then must transfer/redirect that horizontal speed vertically very quickly to maximize jump height. Research on Australian Rules Football players also found that better change of direction was associated with higher reactive strength (Young et al., 2015). Pitching is similar to these movements. Build up a lot of linear momentum and then abruptly stop and transfer that energy in a different direction to maximize output.

Measuring Reactive Strength 

Reactive strength is measured using the reactive strength index, which is simply jump height divided by ground contact time.

RSI = Jump Height/Ground Contact Time

This can be done via a contact mat, other technology or apps measuring RSI itself, or slow-motion video where you count frames to calculate flight time and divide that by ground contact time. This is typically done using a drop jump or repeated hop test. The drop jump is the most common test and would be performed by stepping off a box, hitting the ground, and jumping as high as possible. The legs should remain straight during the flight phase in order to not disrupt the flight time data. The ground contact time should not be allowed to exceed 250ms. If you are comparing these numbers between athletes or over time, make sure you are performing your drop jumps from a consistent height. Height can be experimented with to find what is optimal in terms of RSI.

This first video is a depth jump from a 20″ box and the RSI is 2.2.

The second video is a depth jump from a 12″ box and the RSI is 2.8.

According to Eamonn Flanagan, a leading expert on RSI, the following scores correspond to various levels of reactive strength.


RSI Performance Implications
<1.5 Athlete has low reactive strength. Needs to get stronger. Low level, extensive plyometrics may be used.
1.5-2.0 Athlete has moderate reactive strength. Intensive means are still inappropriate. Reactive strength is an area of opportunity for improvement.
2.0-2.5 Solid level of reactive strength. Intensive means may be used.
>2.5-3.0 High reactive strength. Reactive strength may no longer present an opportunity for sport performance improvement.
>3.0 Elite reactive strength.

Adapted from Flanagan, 2016


Based on the testing an athlete’s training can be appropriately directed from here. 

Training to Improve Reactive Strength


Maximal force capabilities and reactive strength have an important relationship that is often misunderstood. Coaches and athletes have long been recommended that a 1.5xBW squat is a prerequisite for plyometric training. This is an oversimplification of the relationship and unreasonable for many. If this were necessary to prevent injury  young athletes wouldn’t be allowed to sprint or play any type of field or court sports. However, undertaking an intensive plyometric program without a robust strength base is likely a bad idea.

Higher levels of maximal strength have been associated with greater reactive strength (Dymond et al., 2011). This makes sense as higher levels of strength help to increase the strength of connective tissue, such as tendons. In order to quickly transition from landing to propulsion and quickly redirect high forces you must be strong isometrically and eccentrically and be able to display high levels of stiffness to resist deformation. And this seems to make an even larger difference as the drop height increases (Barr and Nolte, 2014). While there is no strength standard for pitchers across the board, a solid strength base (likely above 1.2x BW 3RM squat or so) is recommended given the high ground reaction forces seen at the lead leg-similar to those experienced when dropping from higher boxes.

Extensive Plyometrics

Extensive plyometrics can be used concurrently with training geared towards the development of an adequate strength base. Extensive plyometrics are low amplitude/intensity and are used for relatively high volumes as you progress. The purpose is to build tissue tolerance, get a feel for the rhythm of the movements, and build athleticism as you prepare for more intensive means. Some examples include ankle hopping variations at a submaximal effort, skipping variations at submaximal effort, low box jumps, etc. The key is to keep the intensity lower and build volume with each session.

Intensive Plyometrics and Specificity of Transfer

After a strength base has been built and extensive plyometrics have been used, intensive plyometrics are the next step. Intensive plyometrics are more taxing on the CNS and stressful to connective tissue and are often used for lower volumes. They provide a much more potent stimulus for adaptation but also require more recovery time-somewhere in the range of 48-72 hours between sessions is recommended. Intensive plyometrics are likely to have the most significant impact on RSI in intermediate and advanced athletes. There are both general and specific examples of these movements which should provide varying levels of “transfer” or, dynamic correspondence, as Dr. Bondarchuk would say. You can increase the specificity by using unilateral variations, making them plane specific (frontal plane), making the contact time specific, and adding a second movement with a change of direction. Here are some examples that get progressively more specific.

Drop Jumps-General Intensive plyometric-Bilateral, contact time can be more or less specific depending on height of box and goal of jump

Lateral Bound w/ a Step Off-Frontal plane, unilateral

Lateral Bound w/ a Jump Back-Frontal plane, unilateral, change of direction at second jump


Mechanical interventions are incredibly important when it comes to an effective lead leg, however, the underlying physical capacity must also be present in order for a pitcher to maximize their velocity. Reactive strength is one such quality that may be overlooked, but using the techniques outlined in this article to measure/track reactive strength along with the methods to train this quality, it may become less of a limitation for pitchers.

Interested in training with me remotely or in-person? Contact me and let’s set up a time to discuss your needs and our training options!