Core stability training has become universally accepted as an integral and essential part of many sports conditioning programmes. But just how effective is it? Andrew Hamilton looks at the evidence MORE
Sports injuries: how resistance training can accelerate recovery from back pain
Chronic back pain can ruin athletic performance and even careers. But according to James Marshall, recent evidence suggests that a targeted resistance-based approach can accelerate recovery.
If you haven’t ever suffered from low back pain, you’re lucky. Forty-nine percent of the UK population reports back pain that lasts at least 24 hours at some point each year, and 4 out of 5 adults experiencing back pain at some point in their life(1). What’s more, with 80% of patients, there’s no clear indication as to the cause of this pain(2). This all comes at a cost; in the UK, this is estimated at over £1billion a year in 2000 through loss of productivity and absence from work(3).
For athletes, the cost is in missed training days, missed competitions, missed opportunities for selection and generally getting frustrated. You may be used to training around injuries but a back injury is very debilitating. Light activity and movement is about all you can do when you have acute back pain or spasms.
However, doing nothing at all is not a good route to recovery, and the continuation of normal daily activities is now recommended by medical practitioners for those patients with non-specific causes of low back pain(4). This is preferred to bed rest, which has not been shown to have a positive effect.
Exercise is often recommended by doctors to treat chronic non-specific low back pain (CLBP) and until recently, moderate aerobic exercise has usually been prescribed(8). Other treatments such as thermotherapy, therapeutic ultrasound, massage and electrical stimulation have not been shown conclusively to have positive effects. For athletes however, the use of resistance training allows some form of conditioning to be continued even if sport-specific activities cannot. If the athlete can maintain their body composition, strength and range of movement, then when the pain subsides, the return to sport will be that much easier.
While training the ‘core’ has become a popular focus in recent years, the body does not work in isolation. Lower back pain may be symptomatic of problems elsewhere. So using resistance training (RT) to strengthen the whole body and allow the person to perform activities of daily living (ADL) more efficiently will help reduce stress on the lower back. Aerobic training (AT), which is commonly prescribed for novice exercisers, is good for overall health and body composition maintenance, but does not strengthen the musculature enough to help ADL.
A recent Canadian study compared two different 16-week exercise programmes for patients with CLBP(9). The subjects were split into three groups:
- control group;
- RT group;
- AT group.
Both the RT and AT groups followed a periodised model of training over the 16 weeks, following an undulating pattern of varied resistance or intensity with differing volumes of work. Previous studies have looked at a stepped linear progression of work over a set group of exercises, where the subjects increased the load by incremental amounts when they could cope with the existing workload. It was thought that using a periodised model of training would show greater benefits, as this has been shown in athletic populations to be more effective(10).
The RT used a variety of modes of training, including machines, free weight and body weight exercises. The intensity expressed as a percentage of 1-rep max (1RM) varied from 53% to 72%. The subjects performed 2-3 sets of between 8-12 reps and up to 15 reps of each exercise depending on the week.
Subjects were free to choose the AT training mode of exercise as long as it wasn’t swimming (due to its non-weight bearing nature). The most common forms chosen were the elliptical trainer, and treadmill walking or jogging. Duration of the AT was linked to that of the RT with the total amount per week varying between 60 minutes and 155 minutes. Intensity was gauged using the Borg scale for perceived rating of exertion and varied from 10 to 13. The researchers looked at a variety of fitness and health indices including strength, flexibility, aerobic capacity (VO2max) and body composition. They also assessed the overall quality of life, pain assessment and ability to perform ADL.
The results were fascinating and included the following major gains made in the RT group:
- body fat – 15% reduction;
- muscular strength and endurance – 27% increase;
- power – 14 % increase;
- flexibility – 10% increase;
- reduction in pain – 63%;
- reduction in disability – 67%;
- quality of life (QOL) – 12% improvement.
Previous studies have not shown such significant improvements when RT has been prescribed, so what is different in this study? The researchers determined two main factors:
1. Focusing on the whole body, not just the ‘core’. If you have to use your back to compensate for a weakness elsewhere, making the back stronger may not help. For example, judo athletes who experience back pain may be using too much of their upper body to throw an opponent because their legs are weak. Strengthening the legs and working on technique can ease the pressure on the back.
2. Using periodised programmes. Instead of just working on progressive overload, this study manipulated load and intensity to allow greater adaptations as shown in athletic populations.
The researchers believed that the AT and RT interventions would improve physical abilities and quality of life measurements equally. However, the RT intervention showed greater improvements than the AT group and that is the interesting point because RT is not commonly prescribed as a medical intervention for those people with CLBP. There may be reasons for this, and probably the main one is the lack of suitable supervised sessions available to the general population. Back pain clinics are quite common, if not easily accessible, and tend to focus on core training, but this may not be the most efficient use of time and resources.
Exercises performed in standing
Functional exercises are supposed to be exercises that actually relate to movements in daily life. This compares to non-functional exercises that require movement of a single joint in a single plane of movement. A Canadian study looked at various functional exercises performed in standing and found that overall the muscle activation of any one torso muscle was below 50% of maximum voluntary contraction (MVC) in even the most strenuous exercises(11). An example of the type of exercise measured was the ‘cable walkout’, where subjects walk sideways away from the cable column holding the cable either close to the chest or with arms extended.
The researchers found that although the subjects struggled to maintain form in some of the exercises and felt that they were trying maximally, this was the result of most or all of the torso muscles working together at sub-maximal levels, rather than one muscle working maximally in isolation. This compared to a floor walkout exercise where the subjects started in a press-up position and then walked their hands forward as far as they could whilst maintaining a set back position. Here the rectus abdominis (tummy) muscles achieved 100% MVC, probably because the exercise occurs only in the saggital plane. The other torso muscles work as stabilisers in this exercise to ensure that the body does not tilt left or right or extend, but the rectus abdominus is the prime mover.
The same research group also looked at rowing actions in a different study(12). Rowing actions in a gym can be performed using different equipment types but generally involve the resistance being pulled towards the torso by one or both hands. Here the researchers looked at the barbell bent over row, the standing one arm cable row and an inverted row. For each exercise, the researchers measured the spinal load (the amount of force placed along the spine at different segments) and spinal stiffness (the amount of stability of the spine measured by co-contraction of the torso muscles – the more stiffness there is, the more stable the spine is) as well as muscle activation of all the exercisers.
Each of the three rowing exercises showed different levels of activation and stiffness along the spine. The bent over row showed the highest levels of spinal stiffness, with the lumbar and thoracic spine being activated evenly. This is an exercise where the spine is in a compromised position, so is not recommended for those people who have lower back pain already. However, it’s a good exercise for the athletic population because it does challenge the whole back and torso.
The inverted row produced the least amount of joint compression, muscle stiffness and shear forces of the three exercises. It tended to use the thoracic portion of the spinal muscles more than the lumbar spine. This would be a good exercise for those people with lower back pain because of the lower loading forces, but not as good for the athletic population unless there was a specific need to emphasise thoracic spine work.
The one-armed cable row produced less flexion or extension than the other two exercises, but more rotation of the spine, despite the fact that the subjects were instructed to keep a neutral spine. Here the loading of the torso was caused by the subjects resisting the tendency caused by the weight to try and twist the body rather than an objective twist of the torso – ie they kept the spine still while the weight moved. To the casual observer, it looked like there was no twisting, but the internal forces were working to prevent the twist. This would be a good exercise for those people who need to work on twisting actions.
Much more commonly prescribed exercises for the torso are those performed while lying down or kneeling. A group of American researchers looked at a traditional abdominal crunch, a side bridge, a double leg thrust and an abdominal ‘rollout’ using a commercially available product(13). They looked at which exercise isolated the torso muscles from the rectus femoris muscles (a thigh muscle that is used to flex the hip).
The ab rollout exercise limited the activation of the rectus femoris with high activation of the obliques and rectus abdominus. This exercise is similar to the floor walkout in that it only occurs in the sagittal plane (see figure 2,below). However, the researchers did not measure EMG activity of the back muscles in this study, so it is not possible to quantify this as a low-level core exercise. Subjectively speaking, this is a challenging exercise and so would not be suitable for beginners or people with CLBP.
The double leg thrust required the subjects to lie on their back with knees bent at 90 degrees and shins parallel to the floor, before straightening the legs and lowering them until they could no longer maintain contact with the floor with their lower back. This exercise uses the rectus femoris significantly and is considered an advanced abdominal exercise. The work done by the abdominals is one of stabilisation to limit the shear forces caused by the lowering of the legs, which tilts the pelvis forward. This would not be recommended for beginners or for people with CLBP. The side bridge required the least activation of the abdominals, and so could be used for people who are returning to activity. The lack of flexion, extension or rotation in this exercise results in less spinal loading, but also less applicability to sport.
Putting it together
So what does this mean for athletes with low back pain? The evidence suggests that resistance training using whole body exercises rather than just focusing on the core muscles is an excellent alternative method of rehabilitating non-specific back pain. Periodising the training so that intensity and volume are varied seems to be more effective than adopting a linear progression method. However, in order to be able to start a rehabilitation programme effectively for each athlete, it’s important to know how different exercises stress the back in different ways. Exercises such as the side bridge and the inverted row provide some muscle activation with a low spinal load. The bent over row and double leg thrust are suitable for the athletic population because of the high muscle activation they provide, but should not be given to beginners.
Care should be taken with exercise technique because even exercises such as the standing single arm cable row with no visible body rotation provoke rotational shear forces that could aggravate existing injuries. Some sports such as cycling, swimming, rowing, sailing, judo, wrestling and rugby league require the use of the torso muscles in a lying or sitting down position. Most other sports involve standing, running, jumping or throwing\ striking actions, which combine rotation, flexion and extension actions. Exercises in the gym that isolate the torso may therefore be limited in their application to a specific sporting environment; exercises should therefore be chosen that reflect the demands of a particular sport.
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11. JSCR 23 (2) 455-464 (2009)
12. JSCR 23 (2) 350-358 (2009)
13. JSCR 22 (6) 1939-1946 (2008)