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Pattern overload: can strength training make you injury prone?

SPB looks at the biomechanics of machine resistance training, and why it may not be ideal for certain kinds of athletes

As our regular subscribers will know, performed correctly, strength/resistance training is a thoroughly desirable component of any sports training program. Not only can stronger muscles help reduce the risk of injury, the gains in strength and power that result are also beneficial to many athletes – even those engaging in sports, which although primarily endurance in nature, require occasional bursts of power. In addition, more recent studies have demonstrated that strength training can significantly boost muscle efficiency – more technically known as ‘muscle economy’(1).

The changing nature of resistance training

Take a look back and you’ll see that the nature of resistance training has changed considerably over the past 80 years. Almost all of the early books on weight training techniques included only free-weight exercises, with not a machine in sight. In fact it wasn’t really until the late 1970s and early 80s that machine based resistance exercises started to make a real appearance. This was no doubt due to a combination of factors; increased gym usage by relative weight training novices, the reduced cost of machine manufacturing and the growth of the ‘convenience culture’, which so dominates our lives today.

The trend towards machine training was accelerated by companies such as Nautilus, who applied the science of biomechanics to produce machines that were highly efficient at isolating and working specific muscle groups (see this article). With increasing technology and ever lower manufacturing costs, the sophistication, complexity and universal acceptance of single station resistance machines as the way forward became unstoppable. Nowadays, most commercial gyms have come to rely nearly exclusively on machines to provide resistance training, with free-weights relegated to a cramped corner of the gym – and that’s if there are any at all!

Machine drawbacks

So what? If machines get the job done and are easier, quicker and safer to use, then why shouldn’t we ditch those antiquated free weights? Well, think about this. Mother Nature has developed the human body over millions of years into a highly intelligent and efficient machine. As part of that development, our central and peripheral nervous systems have evolved to protect us from unwanted injury by providing natural sequences of muscle recruitment and movement that share the load across as many muscles and joints as possible. This allows muscles to operate as teams, each working muscle making its contribution to any movement at its optimum length, tension and orientation.

Although you don’t consciously have to think about these movements, your brain is ferociously processing information and sending the right electrical impulses to exactly the right muscle motor units at exactly the right time so that by optimally sharing the load across muscles and joints, you can execute these movements efficiently and safely. However, this is stark contrast to most resistance machines found in the gym, where both the axis and plane of the movement is restricted and pre-determined by the machine and its design.

Restricted movements and pattern overload

To help understand the significance of a restricted movement, let’s use a common machine movement as an example – the seated chest press (see figure 1). To work the chest and triceps, the user applies force against the handles, which are connected by levers, pulleys and a chain or strap system to the weights on the weight stack. In nearly all of machines, the handles are pivoted and are confined to move in only one direction. This means the movement at any one point in the range of motion is one-dimensional; i.e. wherever you are in the lifting phase, there’s only one direction in which the handles will move.


Figure 1: Example of seated chest press machine*

During the movement, the user’s hands describe fixed arc, with no variation possible. (*image courtesy of Technogym )


However, natural sequences of muscle recruitment and movement are designed to share the load across as many muscles and joints as possible, and function in three dimensions – ie up/down, backwards/forwards and left/right. This is hardly surprising since we live in a 3-dimensional world. When you perform the ‘free weight’ movement equivalent of the machine chest press (eg dumbbell or barbell chest press), yes it’s true that the overall direction of motion is in 1-dimensional, but the sequences of muscle recruitment are actually operating in three dimensions. This is not only to control the movement and prevent excessive sideways or backwards/forwards motion, but also to find the optimum arc of motion in order to share the load as efficiently as possible across the muscles and joints.

Being able to operate muscles and joints 3-dimensionally (or more accurately with 3 degrees of dimensional freedom) confers another huge advantage over restricted 1-dimensional movement. Research has demonstrated that the nervous system can not only recruit a specific muscle needed to perform a particular movement pattern, but can also selectively recruit specific motor units, or segments within a given muscle and rotate them as fatigue sets in. This is known as ‘asynchronous stimulation’ and is an important mechanism for conserving energy and preventing unwanted overload in specific tissues(2).

Compare and contrast

Given that ‘free’ or 3-D movements enable load sharing and asynchronous stimulation, it’s hardly surprising to find, for example, that the bar or dumbbell path in a free weight chest press is very different to that in most machine chest presses. Firstly, the free movement path tends to describe an arc, whose exact geometry depends on the individual biomechanics of the lifter. Secondly, were you to very carefully analyze the exact bar/dumbbell path, you would discover that even the most elite lifters in the world would never replicate the same path in two consecutive reps. Contrast this with a machine chest press movement. Every single rep follows the exact same pathway as the last, a pathway that is almost certainly not biomechanically optimal for the lifter. The same motor units will fire in the same order regardless of fatigue, and because of the lack of asynchronous stimulation, those units most suited to working in the ‘superimposed’ pattern dictated by the machine will experience fatigue much sooner than when performing the same exercise with free weights. If this pattern of movement is repeated often enough and for long enough, the end result may be ‘pattern overload’.

Pattern overload – RSI for athletes

Readers will be familiar with repetitive strain injury (RSI), which is a well-known phenomenon and describes tissue breakdown and injury due to a well-defined repeated movement – eg wrist injuries in keyboard operators inputting large volumes of data. Pattern overload can be thought of as the athletic equivalent of RSI. Research suggests that pattern overload can be a significant cause of injury in athletes and sportsmen and women, where an athlete trains or competes using one predominant pattern of motion, with little variability in the training routine(3). For example, pattern overload is thought to be a major source of injury with amateur and professional baseball pitchers, quarterbacks, tennis players and golfers, to name a few(4).

However, pattern overload may become a problem with high volumes of repetitive machine training, which often imposes restricted 1-dimensional movement patterns on joints and muscles, leading to sub-optimum or faulty motor recruitment patterns. This restriction in movement patterns imposed by a machine (designed by an engineer who thinks he/she knows what an optimum movement should be) does not sit well with the concept of ‘anthropological individuality’. Everybody is built slightly and uniquely differently (you only have to look around to confirm this!).

Pelvis width, limb lengths, ratio of limb lengths, the flexibility of each joint, muscle strength ratios surrounding each limb, patterns of innervations to the muscles – all are different in every single person. These differences create different ‘optimum’ patterns of motions. Indeed, so individual are these preferred movement patterns that research has demonstrated individuals can be accurately recognized solely on the basis of their preferred kinematic or dynamic movements. In one study, researchers analyzing the kinematic and biomechanical data of the lower extremities of 14 female participants during a single ground contact when landing on the foot were able to recognize each individual subject with 96% accuracy(5).

Ironically however, many athletes with pattern overload induced injuries from their day-to-day training may be advised to take to the gym to perform ‘strengthening work’ and to stick to machine training because ‘it’s safer’. If the machine training imposes a similar restrictive movement pattern on the already overload or weakened tissues, the result can be a worsening of the condition rather than an improvement. For example, field athletes such as javelin throwers frequently suffer anterior shoulder instability as a result of the repeated high-intensity throwing action. A conditioning coach who then prescribes machine chest presses or pec dec work to strengthen the shoulder may actually be helping to reinforce a dysfunctional pattern of movement, making the chance of a future injury more likely, not less. In a similar manner, pattern overload may become an issue among fitness enthusiasts who perform large volumes of machine training without the complementary training required to make for an overall balanced training program. The result is that these repeatedly imposed movement patterns, which may not be biomechanically well-suited to the user in any case, can lead to instability and injury problems, particularly in the shoulder and lumbar regions.


Practical advice

Although the data is limited, the findings to date suggest that athletes who tend to perform one predominant pattern of motion during their training and competition would be advised not to repetitively train those same muscle groups using machine weights. For example, a rower who has to perform a rowing action involving the back and biceps in a seated position, would not be advised to try and develop strength using a seated row machine, but instead employ free weight movements such as bent over dumbbell rows/deadlifts/supine pull ups etc. That’s not to say machines should not be used; rather that they should be used with an understanding of the limitations for certain individuals in certain circumstances. If free weights are limited or unavailable at your gym/training facility, here are some tips that can help you get the best from them while avoiding the risks outlined above:

  1. Avoid using machines that are ergonomically incorrect for your body. If you find that you just can’t seem to get a machine to fit your dimensions or to ‘feel’ right, no matter how you adjust it, the chances are that it’s just not biomechanically suited to your body. Leave it out and if possible replace it either with a cable or, better still, a free-weight exercise.
  2. Cycle your machine training. Don’t use any one machine more than twice a week, or for more than four consecutive weeks at a time. Alternate your machine exercises either with free weight/cable alternatives, or with another machine. So for example, if you train three times a week, make sure that a) one of those workouts uses either free weights or a totally different type of machine for each body part compared to the other two, and that b) after four weeks, you switch to a completely different routine for the next two to four weeks, where none of the machines used previously are included. This decreases the chance of injury by allowing a healing response in the fatigued or traumatized tissues related to a specific pattern of motion imposed by a machine.
  3. Don’t let the controlled 1-dimensional movement provided by a machine tempt you into trying to perform an excessive range of movement. Research shows that challenging joints with an extreme range of movement under load can stretch the joint capsule and ligaments, leading to faulty neuromechanical control of the joints and a greatly increased risk of future injury(6). Examples of this are lat pull over and leg press machines, which can stretch and destabilize the shoulder and spinal/sacrum joints respectively.
  4. Never train any region of the body in pain. Pain invariably causes inhibition of the stabilizing muscles, which cross the joint. Training while in pain will result in progressive instability in the affected joint.
  5. Get advice! If you suffer or have previously suffered from a chronic or instability type injury, seek professional advice before putting together a machine program. The affected areas will almost certainly more vulnerable to pattern overload injuries unless appropriate stability training is undertaken first.
  6. If your current gym only offers a limited selection of fixed path machines and no free weights despite being swish and high-tech, consider switching gyms! Remember – not everything in this modern world of ours is all it’s cracked up to be!

References

  1. J Funct Morphol Kinesiol. 2021 Mar 17;6(1):29
  2. Front Neurosci. 2016 Sep 13;10:414
  3. Medicina (Kaunas). 2010;46(6):365-73
  4. Schmidt R., Motor Learning and Performance (p. 178), Human Kinetics, 1991
  5. Gait Posture 2002;15:180-6.
  6. BMJ Open Sport Exerc Med. 2018 Jul 17;4(1):e000382

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