Part 3: Testing & evaluating special strength:
With a basic overview and understanding of various neuromuscular adaptations to training, the next aspect which we will look at, is the evaluation of our athlete’s ability to express power as well as what best practice is to improve it.
Samozini et al, recently published a study on an iPhone app that allows you to not only determine jump height through flight time but also build a force-velocity profile on your athletes (see figure 1).
Apps like this are very useful, as they are cost effective, portable, valid and reliable – see link to open source;
They allow strength and conditioning specialist to conduct scientific analyses on their athletes with ease, they allow strength and conditioning specialist to conduct scientific analyses on their athletes with ease, and in-turn they gather valuable information from it to allow for better program prescription.
But before we move on, let me introduce you to a few terms that are synonymous with explosive power:
- Starting Strength: The muscles ability to produce force at the start of the contraction before any external movement occurs.
- Acceleration Strength: The ability to produce Fmax force as quickly as possible at the start of and isometric or concentric contraction.
- Index of Explosive Strength (IES): Is an expression of the of the athletes ability to produce maximal force in the shortest time period. IES = Fmax / Tmax
- Rate of Force Development (RFD): Rate of rise of contractile force at the onset of a muscle contraction. RFD = Fmax (A) – Fmin (B)/ Time from A – B
- Reactivity Coefficient (RC): Is the athlete’s explosive strength index relative to their body weight. RC = Fmax / Tmax . W Or RFDmax / W
- Reactive Strength Index (RSI): The athlete’s ability to produce a maximal concentric contraction in the shortest period of time that is preceded by an eccentric contraction. RSI = Fmax – Fmin / Contact Time
- Strength Deficit: The difference in force production between movements incorporating the stretch shortening cycle and movements predominantly utilizing the concentric contraction.
When training for explosive strength we need to consider all the above components of explosive strength, i.e. taking into account the athletes specific neuromuscular structure that is required to produce maximal force as quickly as possible. However, if one of the “links in the chain” is missed, then the expression of Fmax will not be entirely possible. Therefore, when programming with an end goal of explosive strength in mind, we have to consider the full spectrum of strength and power training to ensure that our athletes reap the rewards of true training transfer.
What are some of the methods used to evaluate explosive strength?
Although it is beyond the scope of this post to discuss all the possible methods of testing explosive strength in detail, I will aim to briefly address some of the most utilized methods in mainstream strength and conditioning.
One of the easiest methods of testing your athlete’s strength deficit is by calculating the difference between a countermovement jump height and squat jump height. This will allow the strength and conditioning professionals to identify the areas that their athletes need to work on. For example, a large deficit may indicate that more hypertrophy or strength development is required, whereas a smaller deficit may indicate that more stretch shortening cycle type work is required (See figure 3).
The use of more expensive equipment such a the GymAware, Fitrodyne, force plates or contact mats allow for many different explosive strength test to be conducted. For example, strength and conditioning coaches are able to create force velocity and power curves with various lifts, such as squats, squat jumps, clean variations, bench press etc, to establish the neuromuscular development of their athletes.
Reactive Strength Index testing is another good measure that can be conducted using a force plate or contact mat. Depth vertical jumps from various heights (e.g. 30cm, 45cm & 60cm) will give you an overview of the reactive strength and neural firing rates of your athletes. This is important because a decrease in neural firing rates will cause a decrease a particular joint stability. The longer it takes for the muscles to contract in a dynamic environment the more susceptible your athlete is to ligamentous injuries.
Rate-of-force development and starting strength can be measured on a force plate with various movements such ad isometric mid-thigh pulls, counter-movement-jumps and squat jumps, just to name a few.
Lastly, some more common test that are used to identify athlete explosive strength with equipment that is more accessible are tests such as; medicine ball chest throws, medicine ball overhead throws, broad jumps as well as vertical jumps.
Developing maximal neuromuscular power; Part 1: Biological basis of maximal power production; Cormie et al; 2011
Developing maximal neuromuscular power; Part 2: Training considerations for improving maximal power production; Cormie et al; 2011