BBC (Broad Biomechanical Correspondence) Technology - the effect of varying pin settings on the operation of MyoQuip machines

MyoQuip's BBC Technology is designed as a compensation mechanism for biomechanical disadvantage. When a limb is fully flexed, i.e., the foot or hand is close to the trunk, the muscles of that limb are operating in a position of considerable biomechanical disadvantage, but as the limb extends away from the trunk it moves into a progressively more biomechanically efficient orientation.

An example of this changing biomechanical efficiency can be seen with the barbell squat. When the hip and knee joints are flexed as in the deep position of the squat, the lifter's capacity to cope with resistance is considerably reduced; but as they rise and the joints fully extend, the amount of resistance that can be coped with increases dramatically. This is why there is a very strong tendency for unsupervised and inexperienced lifters to perform only partial squats and why the squat does not effectively work the leg extensor muscles through their full range.

MyoQuip's machines such as the MyoThrusta and the MyoTruk use Broad Biomechanical Correspondence Technology to provide increasing resistance throughout the exercise movement. This enables the exerciser to operate comfortably and effectively in the region of biomechanical disadvantage. In addition the technology exposes them to substantial effective loading and high-range muscle fibre recruitment throughout the whole range of movement.


BBC technology is an easily adjustable form of accommodating resistance. The rate at which the effective resistance changes is varied by selecting different pin positions on the machine's adjustment bar.


Mid-range pin settings

These are designed to broadly compensate for the improvement in biomechanical advantage throughout the exercise movement. The increase in effective load from the start of the movement to full lockout is intended to match the body's capacity to handle resistance, so that the exerciser has to expend basically the same degree of effort throughout the movement; in other words to provide broad biomechanical correspondence between the exerciser's load-bearing capacity and the effective load. This can be contrasted with the barbell squat where considerable effort is required at the bottom of the movement and very little at the top end.

Thus with a mid-range pin setting on apparatus such as the MyoThrusta the leg extensor muscles experience substantial activation throughout the whole range of movement.

Low-range pin settings

Here the increase in effective load from start to finish of the exercise movement is greatly increased. These notch settings are ideal for practising explosive or ballistic movements. The exerciser chooses a weight load they can comfortably handle at the start of the movement and then attempts to perform the concentric part of the exercise as rapidly as possible. However, as they move toward full leg extension the effective load is rapidly increasing thus slowing their momentum. As a result there is a "ballistic braking" effect toward the end of the movement, eliminating the need to decelerate. Because of this the exerciser can utilise explosive strength over the full range of the movement.

This range of settings is particularly useful with the MyoThrusta where concentration on plyometric-type movements can be expected to produce significant improvements in vertical leap.

High-range pin settings

The increase in effective load from start to finish of the exercise movement is greatly reduced. High pin settings are ideal when the focus is on overcoming inertia, i.e., moving a heavy load from a position of rest. A typical real world application is in rugby when there is the need to "shunt" the opposing pack. A similar situation applies in the rugby lineout when a lifter with poor vertical jumping ability has to be rapidly hoisted.

High-range pin settings are also useful when the MyoTruk or MyoThrusta is being used to improve performance in the barbell squat, because the additional loading at the start of the movement conditions the leg extensors to operate more effectively in the region of greatest biomechanical disadvantage, e.g., in the deep squat position.
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Bands, chains and broad biomechanical correspondence

[Summary: The addition of bands or chains to free weights permits adjustment of the resistance to the muscles' load-bearing capacity throughout an exercise movement. This broad biomechanical correspondence allows exercises to be performed explosively over their full range, effectively conditioning the body for actual sporting and athletic activities. The development of sophisticated mechanisms employing the same principle has important implications for sport-specific strength development.]

There are two main types of variable resistance exercise equipment:

Close biomechanical correspondence

Manufacturers of cam-driven machines claim to vary their resistance to closely match the torque curves of natural joint movements. In other words they assert a close biomechanical correspondence (CBC) between resistance and muscular capacity. However, given the variation between individuals in relative limb lengths, muscle attachment points, genetically endowed strength relativities between various muscles, etc., it is doubtful that such claims of accurate correspondence between load and load-bearing capacity are justifiable.

CBC machines are basically designed for single-joint movement of isolated muscle groups performed at a measured pace. Their very limited applicability to sports training is highlighted by Zatsiorsky's comment: "The important limitation of many strength machines is that they are designed to train muscles, not movement."

Broad biomechanical correspondence

The other type of variable resistance apparatus does not attempt to achieve any precise correspondence between resistance and muscular capacity.Rather the rationale for their use is that substantial benefits are achievable from load variance so long as the changing load-bearing capacity of the muscles involved is approximated. Bands and chains are examples of apparatus that rely only on such broad biomechanical correspondence (BBC).

In operation heavy rubber bands or steel chains are attached to either end of a loaded barbell and anchored to the floor or other fixed points. This enables a progressive increase in resistance for exercises such as squats and bench presses. A distinguishing feature of these exercises is that they are heavy load and involve multi-joint or whole limb movements.

The deceleration problem with free-weight exercises

Explosive strength is fundamental to many sporting or athletic activities but free weights are defective in building explosive strength. In the squat or bench press, for example, various studies have shown the bar decelerating for much of the final section of the range of motion. In the deceleration phase there is significantly decreased motor unit recruitment, velocity of movement and power production. In addition, when free weight movements are performed forcefully, antagonistic muscle action takes place to slow down and halt the limb to avoid soft tissue rupture or joint dislocation.

Conditioning the muscles for deceleration during the final stage of an exercise movement is counterproductive if the objective is to enhance ballistic-type sporting actions like throwing or jumping. This is also true where there is an inertia-dissipating or energy-absorbing mass to be moved, as in tackle engagements in football. Similar dynamics apply at the line of scrimmage in American football or in a rugby union scrum. In each of these cases the appropriate simulation is an acceleration through the whole range of limb movement.

Adding BBC characteristics to free weights enables exercises to be performed explosively or ballistically with the progressively increasing resistance providing a braking effect. Peak power occurs near the extreme points of angular motion.

A new generation of BBC machines

Recently MyoQuip have introduced a new system of lever and fulcrum technology that achieves the same basic effect as bands and chains but permits the development of sophisticated mechanisms with a high degree of specificity to particular sporting activities.

Because of their primitivity the use of bands and chains has largely been restricted to the power-lifting community. A major limitation of the equipment has been the difficulty in incrementally changing load. The fixed load component can be readily altered by adding or removing weight plates, but there is no way of making minor adjustments to the variable element provided by bands or chains.

With MyoQuip's machines, incremental load changes are effected simply by adding or removing weight plates, and the rate at which the load changes during a movement can be altered by choosing a different pin setting.

The MyoQuip technology also permits considerable flexibility in the orientation of effort. For example, the ScrumTruk machine is operated in the horizontal rather than the vertical plane, while the HipneeFlex, which is used to develop the leg flexor muscles, is configured for decreasing instead of increasing resistance.

The further development of machines delivering full-range muscle activation in either extension or flexion across multiple joints is likely to have important implications for strength training for sport.
bands
chains
biomechanical
multi-joint
explosive strength
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