Basic Bio-mechanics: Terms and Definitions

Basic Bio-mechanics: Terms and Definitions

Bio-mechanics is a fascinating field. Possessing sufficient knowledge in this area is paramount for properly understanding resistance training. I try my best to educate my readers so that over time they can build upon their knowledge and reach superior levels of understanding with regards to human movement.

I have listed some definitions below that I would like for my readers to try to familiarize themselves with as it will allow them to better comprehend future blog-posts, articles, videos, and interviews. I created a special tab on the right hand column of the blog named “Bio-mechanics Terminology” so you can find this particular article whenever you need it.

Force: force equals mass times acceleration and is a vector quantity, meaning that it’s displayed in a particular direction. Force is usually measured in Newtons.

GRFs: GRF stands for ground reaction force. When you jump, sprint, or perform an Olympic lift, you exert force into the ground. Force-plates measure these forces. During vertical jumping, most of the force produced is vertical. However, in sprinting, you have vertical forces as well as horizontal forces. When the foot strikes the ground during maximum speed sprinting, at first the force is projected forward which is called braking forces, and once the COM passes over the foot, the force is projected rearward which is called propulsive forces. In general, force, including GRF, is measured in Newtons.

Muscle Force: when muscles contract or are stretched, they create muscle force. This muscle force pulls on bones which creates joint torque. In general, force, including muscle force, is measured in Newtons.

Velocity: velocity is the rate of change of position of the athlete. It’s just like the term speed, but with a direction associated with it. It is usually measured in meters per
second, but can also be expressed in miles per hour or kilometers per hour.

Vector: vectors contain both magnitudes and directions. Force, velocity, and acceleration are all vector quantities.

Force-Velocity Curve: you can plot the force-velocity curve on a graph by plotng force on the y-axis and velocity on the x-axis. In strength & conditioning, the goal is to shift the curve upward and to the right so that the athlete can exhibit more force and power at every possible load. Heavy strength training tends to shift the curve more on the force end of the spectrum, whereas explosive training tends to shift the curve more on the velocity end of the spectrum.

Joint Angular Velocity: joints in the human body move through arcs and therefore accelerate through a range of angular motion. Joint angular velocity is the rate of change of joint movement, often measured in degrees per second or radians per second.

Acceleration: acceleration examines the rate of change of velocity with respect to time, and is typically reported in meters per second per second (meters per second
squared).

Power: power is the rate of doing work. It is calculated either by dividing work by time, or by multiplying force by velocity. Power is usually reported in watts.

Joint Power: it is possible to measure the power output of individual joints during movement by multiplying the torque by the joint angular velocity. It is usually reported in Newton-meters per second.

RFD: RFD stands for rate of force development and can be measured in multiple ways. RFD is believed to be highly important in sports that require rapid force generation. It is usually measured in Newtons per second.

RTD: RTD stands for rate of torque development and is usually measured in Newton-meters per second.

RER: RER stands for rate of EMG rise and represents the rate of increase in muscle activation. RER is typically measured in % of MVC per millisecond or millivolts per second.

Impulse: impulse is force multiplied by time (actually it’s the sum of net force, or the force that influences acceleration, multiplied by time over a phase of interest), and is sometimes calculated by taking the area under the forcetime curve. It is typically reported in newton-seconds.