slow motion study of the human body ballistically swinging a heavy kettle bell with maximal acceleration and deceleration
Video on April 20, 2013
Resistance: 36 kg (79.2 lb.) kettle bell
Bodyweight: 81.4 kg (179 lb.)
Static load to bodyweight ratio: 0.44:1 (or 44.4%)
The movement is captured from three camera angles: side, front, and rear. The first clip presents the side view at real-time speed, the second clip is from the side in slow motion (20% of real-time speed), the third clip is from the front in slow motion, and the fourth clip is from the rear in slow motion. Note: for video of real-time speed from the front see this.
physics and dynamics
Observe how the energy flows through the body’s kinetic chain during the accelerative and decelerative phases as different muscle groups contract and relax in sequence. Note that hip flexion and knee flexion are strongly engaged (“pulling”) in addition to hip extension and knee extension (“pushing”). I cannot think of any other movement that recruits full body pulling and lower body pushing anywhere near this degree; it is achieved because the inertia of the kettle bell creates a large additional force in addition to gravity whose force vector is around 30 to 40 degrees greater than orthogonal to the gravitational force and pointing away from you (i.e. pulling you forward). This is the force you are pulling against when you decelerate and reverse the direction of the kettle bell (the kettle bell is always under the influence of the gravitational force throughout the bi-directional trajectory.) Trunk stabilization with both the abdominal complex and their antagonists the erector spinae are at a premium to manage the dynamic load. The entire body is severely challenged to maintain balance via proprioception. If balance is lost it is very difficult to recover and the kettle bell often must be released to avoid falling forward or flying backward. This movement imposes a great training effect for enhancing agility (systemic, dynamic motor control). It is a neurological tour de force.
A normal kettle bell swinging movement does not emphasize maximal acceleration and deceleration of the load through the full range of movement (it is a focus only on explosive hip extension). When you introduce the additional dynamics, this movement is dramatically different physically and mentally.
Mentally it feels the same as doing an Olympic clean or snatch with the focus on maximal velocity and maximal explosiveness to overcome inertia. However, with this movement, there is both a pull and a push, not just a push as in Olympic movements: active deceleration eliminates the “free ride” effect created by the explosive acceleration ( i.e. the rapid switching of the magnitude and direction of the force vector at both endpoints affects entire body control dramatically). What this means is that even though the kettle bell is moving outward and is still accelerating from hip extension you are simultaneously braking it with full lat and ab/core recruitment well prior to the return or inward trajectory of the kettle bell. Complementary musculature must be fully engaged with 100% duty cycle in order to reduce the cycle time (time to execute one rep) to a minimum.
Physically, there is a powerful engagement of the abdominals, other core muscles and the latissimus dorsi that is lacking without the dynamics (there is no “free ride” of kettle bell travel anywhere in the range of motion). Exhalation is in the outward movement and inhalation during the inward movement but a significant amount of your inhaled air must be retained to maintain outward pressure on the diaphragm in order to keep the torso stiff like in a squat when coming out of the bottom. Additionally, because each cycle is only one second in duration and the breathing is synchronized to movement, you must exhale a significant air volume in one-half second which immediately switches to the inhalation phase of only one-half second. Because of the metabolic power demand of this movement and the constrained breathing requirements, this is necessarily a noisy exercise during a maximal effort!
the bi-directional force vector of the kettle bell ballistics
A good way to think of this phenomena is the internal and external ballistics of a bullet shot out of a gun. The bullet is falling due to the force of gravity the instant it leaves the barrel. But why is the bullet moving so fast horizontally? Gravitational force only acts downward; the horizontally directed energy is from the explosion of the gun power which produces a force that acts on the mass of the bullet inducing an acceleration; deceleration is caused by drag forces. In conventional weight lifting there is only constant velocity (so acceleration = 0) and resistance is provided by gravitational force only. In Olympic movements you do have acceleration but deceleration is not a major feature (the load is literally dropped in competitions and in the gym it is lowered under control or dropped: deceleration is not part of the organism’s adaptation to stress). In kettle bell training there is no emphasis on maximal ballistics and certainly not on deceleration.
In this movement you have muscular “gun powder” producing ballistics outward (30 degrees above horizontal) and instead of the bullet or the Olympic barbell crashing to earth you are using muscular energy (“drag force”) to decelerate a rapidly accelerating 36 kg bullet and pull it back reversing the outward trajectory to an inward one. This is an additional training stimulus not featured in any form of conventional or Olympic lifting.
So, what is unique about this movement is the emergence of a large second force vector (a horizontal component) in addition to the gravitational force vector due to the acceleration and deceleration of a mass (the kettle bell) of approximately one-third of your body weight (your body “weight” really is the force on your body mass due to gravity) at terminal velocity and very near the magnitude of the kettle bell’s gravitational force vector (the static kettle bell “weight”). The static load of the kettle bell (force due to gravity or the gravitational force vector) is 352.8 N (Force = Mass x Acceleration or 36 kg X 9.8 m/sec^2) but the dynamic load is a significant percentage of the static load and is directed at a angle of about 30 degrees above orthogonal (i.e. 30 degrees above a right angle to gravity or 120 degrees) to the gravitational force vector and is pointing outward from your body. The significance of this is that the large inertia of this second, emergent, dynamic force is the one you pull against to cause deceleration during the path of the kettle bell as it approaches terminal velocity moving outward and then reverses direction to move inward.
Note: 5 cycles (“reps”) were completed in 6 seconds for a time of 1.2 sec/cycle.
I learned about this movement from a video by Mike Visscher in San Diego, CA at www.ignitionfitness.com.
For more information:
BIONX SUPERMODEL (pdf)