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.
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MyoQuip launches the HipneeFlex - hip and knee flexor strength builder

After extensive prototype testing, MyoQuip is proud to release the HipneeFlex, a truly unique apparatus for the development of the hip and knee flexors.

The HipneeFlex permits the hip flexor and knee flexor muscles to be exercised simultaneously through the full range of leg movement from full extension to full flexion. Both sets of muscles are subjected to substantial but appropriate loading throughout the whole movement.

Figure 1 shows the basic mechanism of the HipneeFlex. The athlete operates from a supine position so that the action of the flexors - iliopsoas and hamstrings for the hip and knee joints respectively - can be effectively isolated. The feet are engaged between rollers which are cable-connected to the weighted QuadTorq mechanism.

The exercise movement involves the feet being drawn back from a fully extended position to a fully flexed position. Thus both hip and knee flexors are exercised through a range where the included angle at the joints varies from 180º to around 30º.

The arc through which the foot engagement device moves is designed to closely parallel the path that the feet would normally traverse if drawn back without resistance. It also creates a natural tendency for the two joint angles to vary synchronously so that they are both under continual load.

Biomechanical correspondence In going from full extension to full flexion the limb joints are moving towards a progressively inferior biomechanical orientation and consequently, less capacity to handle load.In view of this the QuadTorq mechanism for the HipneeFlex is configured for decreasing resistance. (This is opposite to MyoQuip's other machines, the ScrumTruk, JumpTruk and HipneeThrust. Because they involve limb extension rather than limb flexion their QuadTorq orientation is for increasing resistance.)

Hamstring development It could be argued that other exercises and apparatus cater adequately for hamstring development. For example, in their role as hip flexors, they are strongly activated in whole-leg extensor movements such as the barbell squat. But with regard to their other function as knee flexors the most commonly used apparatus, the leg curl machine, doesn't usually involve knee joint closure much below 90º and it is also a simple single-joint exercise. By contrast, many of the important sporting activities involving the knee flexor, such as sprinting, cycling or rowing, produce acute joint angles and also require complex coordination between the hamstrings and iliopsoas. The HipneeFlex is the only strength apparatus that effectively simulates that coordination.

Hip flexor strength and sport The most widely recognised sport-related function of the iliopsoas is in enhancing knee lift in sprinting. They also play a vital role in football kicking, swim kicking and sports such as rowing.

Iliopsoas strengthening has specific performance implications for cycling which involves continuous though offsetting leg extension and flexion. Enhanced hip flexor capacity has particular relevance to the cycling upstroke where both hip and knee joints are flexing. Concentration on using the hip flexors takes load off the hamstrings, the most overworked muscles in cycling.

Cross country skiing is particularly taxing on the hip flexors, as are other activities involving vertical movement of the body such as cross country running and mountain climbing.

Some of the more athletic forms of dance necessitate very strong hip flexors.

More generally, in any sporting activities requiring hip joint extension, the hip flexors perform a crucial antagonist function.

Tight hip flexors are recognised as contributing to lower back pain by causing the pelvis to tip forward. Full range activation of the iliopsoas through use of the HipneeFlex can be expected to have a beneficial effect on flexor flexibility.

Hip flexor development Until now the hip flexors have been the most neglected muscle group in strength training. Now with the release of the HipneeFlex there is a machine that has significant specificity to natural movement of these muscles, that involves their full range activation and that has a high degree of biomechanical correspondence between effective load and load-bearing capacity of those muscles at a particular limb position.

Athletes and their coaches constantly seek minor improvements that could conceivably give them a competitive edge. Here we have an apparatus that can safely and effectively strengthen a muscle group that is intrinsically involved in many athletic and sporting activities but which is virtually never developed to its full potential.

No one really knows the extent of the benefits that will flow from eliminating that imbalance.



We invite you to be one of the first to explore the potential of really strong hip flexors. Alternatively, you can wait and then play "catch-up" with the rest of the herd.

If you are located outside Australia please use the email link in the sidebar to obtain a quotation in your own currency including shipment options.

(See also my previous post, Hip flexors - the most underdeveloped muscle group in strength training.)
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Hip flexors - the most underdeveloped muscle group in strength training

[Summary: Strong hip flexors provide an advantage in a wide range of sports and athletic activities but they are the most neglected muscle group in strength training. The problem in developing hip flexor strength has been the lack of appropriate exercises, but the development of flexor-specific apparatus offers great potential for fully developing these muscles.]

Despite their importance to a wide range of athletic and sporting activities, the hip flexors are the most neglected major muscle group in strength training. It is very rare to find training programs that include hip flexor exercises. By contrast there is usually a great deal of emphasis on exercises for the leg extensors.



There are some obvious reasons for this comparative neglect. The principal muscles involved in hip flexion are the psoas and the iliacus, collectively known as the iliopsoas. Because they are relatively deep-seated rather than surface muscles they may have been overlooked by bodybuilders who have traditionally been the major innovators in strength training. Secondly, there are no obvious ways to adequately exercise them with free weights. Finally, these muscles do not have the obvious functional importance of their extensor counterparts. Yet, as antagonists, both hip and knee flexors perform a vital role in controlling the rate of descent and ascent in leg extension exercises such as the squat.

There is no corresponding problem of underdevelopment with the muscles responsible for knee joint flexion, the hamstring group. Because they cross two joints they are active in both leg extension and leg flexion. They act to flex the knee joint and also to extend the hip joint. Therefore they tend to be strengthened by complex leg extension exercises. Also hamstrings can be developed and strengthened through the use of the leg curl apparatus.

Strong hip flexors provide an advantage in a wide range of sports and athletic activities. In sprinting high knee lift is associated with increased stride length and therefore considerable attention is given to exercising the hip flexors. However, they are usually not exercised against resistance and consequently there is unlikely to be any appreciable strength increase.

Hip flexor strength is directly relevant to a range of activities in football. Kicking a ball is a complex coordinated action involving simultaneous knee extension and hip flexion, so developing a more powerful kick requires exercises applicable to these muscle groups. Strong hip flexors can also be very advantageous in the tackle situation in American football and both rugby union and rugby league where a player is attempting to take further steps forward with an opposing player clinging to his legs.

In addition those players in American football and rugby who have massively developed quadriceps and gluteus muscles are often unable to generate rapid knee lift and hence tend to shuffle around the field. Having stronger flexors would significantly improve their mobility.

It is commonly asserted that marked strength disparity between hip extensors and hip flexors may be a contributing factor in hamstring injuries in footballers. It is interesting to speculate on whether hip extensor/flexor imbalance might also be associated with the relatively high incidence of groin injuries.

Other sports where increased iliopsoas strength would appear to offer benefits include cycling, rowing and mountain climbing, in particular when scaling rock faces.

The problem in developing hip flexor strength has been the lack of appropriate exercises. Two that have traditionally been used for this muscle group are incline sit-ups and hanging leg raises, but in both cases the resistance is basically provided by the exerciser's own body weight. As a consequence these exercises can make only a very limited contribution to actually strengthening the flexors.

Until now the only weighted resistance equipment employed for this purpose has been the multi-hip type machine. When using this multi-function apparatus for hip flexion the exerciser pushes with the lower thigh against a padded roller which swings in an arc. One difficulty with this apparatus is that the position of the hip joint is not fixed and thus it is difficult to maintain correct form when using heavy weights or lifting the thigh above the horizontal.

With the release of the MyoQuip HipneeFlex there is now a machine specifically designed to develop and strengthen the leg flexors. It exercises both hip and knee flexors simultaneously from full extension to full flexion. Because the biomechanical efficiency of these joints decreases in moving from extension to flexion, the mechanism is configured to provide decreasing resistance throughout the exercise movement and thus appropriate loading to both sets of flexors.

The absence until now of effective techniques for developing the hip flexors means that we do not really know what benefits would flow from their full development. However, given that in elite sport comparatively minor performance improvements can translate into contest supremacy, it is an area that offers great potential.

(See also my follow-up postMyoQuip launches the HipneeFlex - hip and knee flexor strength builder.)
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