Rate of Force Development (Early versus Late)

Rate of force development (RFD) can be broken down into two stages. There is an early stage rate of force development and a late stage rate of force development.  Early stage RFD is typically measured from 0-100 ms while late stage RFD is anything after.

Importance of Early Stage RFD

Sporting movements are often required to be fast, reactive movements that occur over a small amplitude. For example a large countermovement jump can take between 500-1000ms, while a squat jump with no countermovement may take around 300 to 430ms (1). In sport, movement amplitude is going to be much more similar to that of a squat jump (zero to minimal countermovement) than to that of a large CMJ. At the same time, sprinting ground contact times can last as short as 100ms. With this in mind, it is easy to see how early RFD may play an important role in sporting movement, especially those covering a small amplitude over a short period of time (ranging from 100-430ms).

Continue reading “Rate of Force Development (Early versus Late)”

Muscle Slack


Frans Bosch has popularized the concept of muscle slack (Van Hooren has publications on it). It is hinges on early stage rate of force development and the speed at which the muscle, tendon, and series elastic element can go from “slack” to “tense”. When a muscle is not activated, it is relaxed and there is slack in the muscle, tendon, and series elastic element as it hangs from its origin and insertion. Bosch uses the analogy of a rope to help describe how muscle slack works. You are holding one end of the rope and the other end is tied to a car, you are the origin and the car is the insertion. Before you can pull the car with the rope, the rope first has to become tense. This is the point where the rope goes from lying slack on the ground, to now in a straight line from your hands to the car. This is synonymous with the process of the muscle fibers aligning from the origin and insertion. The second part of the slack is that the rope now needs to become tense enough so that force can be applied to the truck. At this point, the rope goes from being in a straight line from your hand to the car, to now taut, from you producing a force on the rope. This is synonymous with the muscle co-contracting to produce enough force on the tendon so the muscle can become tense. Muscle slack uptake occurs during start of where the contractile element receives the chemical signal to align all the way to the point where both the musculotendon unit and the series elastic element are tense.

Continue reading “Muscle Slack”

Muscle Slack and High Velocity Training: An Integrative Approach

Velocity Deficient


The idea of measuring and training for velocity deficiencies has become popular since the recent studies of JB Morin and colleagues. In one of their studies, they examined several different subjects and based on their profiling methods, determined whether or not the individuals had a force-velocity profile that was either velocity deficient or force deficient. Once the deficiency was determined, the subjects were trained using specific methods emphasizing the velocity component of the movement (slow velocity for max force and fast velocity for speed of movement). After the study’s training cycle, J.B Morin and colleagues were able to show that the specific training methods, either slow or fast, improved vertical jump performance and overall balance of the subjects’ force velocity profiles.

Continue reading “Muscle Slack and High Velocity Training: An Integrative Approach”

Developing Explosive Power: Slow Speed Strength


Strength is contextual. In movement, force (strength) can be produce at all speeds. For example, high-speed strength means being able to produce large amounts of force at a high velocity. Slow speed strength simply means being able to produce high amounts of force at low velocities. At all times, when talking about strength, we need to make sure that the context is clarified. However, just because they are contextually different, does not mean they are not related. For example, increasing slow speed strength (one rep maxes) can help facilitate high speed strength (vertical jump height).

Continue reading “Developing Explosive Power: Slow Speed Strength”

Bands versus Chains

Accommodating resistance is widely used in strength training (for more detail on accommodating resistance click here). However, not all accommodating resistances used (bands versus chains) will result in the same stimulus. Both bands and chains accomplish a similar goals (add resistance throughout the movement), but their influence on the kinematics of the movement are different.

Why use accommodating resistance (Short Answer)

Accommodating resistance can increase the time force is applied during a movement (increases time of acceleration) and total power of a movement (1). Accommodating resistance adds load to the bar as the athlete moves through the range of the motion of the movement, increasing from the bottom to the top. It does not make all movements “better”. However, when used properly it can add a unique stimulus to the athlete’s training.

Continue reading “Bands versus Chains”

Is There Strong Enough?


There has always been a debate as to whether or not maximal strength is that important, how strong is strong enough, and if not max strength, then what?

It is well documented that increasing maximal strength causes positive adaptations in force output through a wide variety of loads. This carry over from maximal strength to higher velocities is most commonly noted when dealing with relatively untrained athletes. However, as the athlete raises their training state (base levels of strength), such carry over begins to diminish. The brings into question the efficiency of maximal strength training in higher trained athletes and whether or not it is the most beneficial type of training for their sporting performance.

Squat max strength is on the Y axis and the a unit of time is on the X axis. Example of diminishing returns on squat strength and time for improvement (Examples referenced below)

Continue reading “Is There Strong Enough?”

Eccentric Training: Techniques for Added Strength and Size

Author: Jonathan Mike, PhD CSCS*D, NSCA-CPT*D, USAW, NKT-1


When someone or something is described as “eccentric,” it often has a negative connotation. Interestingly, that’s also the case with training programs that emphasizes Eccentric Training. However, the reason is that the eccentric phase of a weight-lifting rep is often referred to as the “negative,” the portion of the rep where the muscle fiber increases in length, or the active lengthening on fibers under load.

Continue reading “Eccentric Training: Techniques for Added Strength and Size”