Lifting tasks and forward flexion movements are often related to lower back problems. It is possible that those who suffer back problems have a different muscle activity pattern during these types of movements than those who have healthy backs. To investigate this further, Leinonen et al examined the electromyographic (EMG) activity of the gluteus maximus (GM) biceps femoris (BF) and paraspinal (PS) muscles during trunk flexion and extension, comparing the EMG patterns of 19 women with lower back symptoms with those of 19 matched control subjects (Leinonen at al, 2000. Arch Phys Med Rehab, 81, pp 32-37).
Each subject performed a controlled trunk flexion forward in the standing position lasting five seconds and then a trunk extension back to upright also lasting five seconds. The EMG activity of the gluteus maximus, biceps femoris and paraspinal muscles was recorded during the whole of the movement. The muscle activity levels and the time each muscle was active and relaxed during the movement was recorded.
The researchers found a general pattern: that during the early phase of forward flexion the paraspinal and biceps femoris muscles were activated together. By the end of flexion, all three muscles were active and during extension all three were also active. However, the key difference between back patients and the healthy controls was the amount of gluteus maximus activity. During flexion gluteus maximus activity was significantly shorter and during extension the gluteus maximus activity ended earlier. This means that the gluteus maximus of the back patients was switching on later and turning off sooner during the flexion extension movement.
The results of this study add weight to the idea that the gluteal muscles in back patients are subject to deconditioning and need to be trained to function normally. Back patients should re-educate the gluteal muscles to be more active during trunk flexion extension movements. More specifically, patients should train the gluteals to be active for longer in order to provide more stability for the lumbar area.
Here's some proof that stretching the hamstrings will reduce injuries
Most of us believe that if you have good flexibility in your hamstrings it will help you avoid injuries. Surprisingly, though, few studies have actually demonstrated this, until now. In this recent study (Hartig & Henderson, 1999, Am J Sports Med, 27(2), pp 173-176) the researchers analysed the incidence of lower-leg injuries in two groups of army recruits going through basic training. The control group, numbering 148, progressed through the same 13-week training programme as the intervention group, who numbered 150. The only difference between them was that the intervention group added three hamstring-stretching exercises to their fitness programme each week.
The main findings were that the intervention group improved their hamstring flexibility during the training period while the control group did not, and the incidence of lower-leg injuries in the intervention group was significantly lower. During the 13-week programme, 43 injuries occurred in the control group, an incidence of 29.1%, compared to 25 injuries in the intervention group, an incidence of 16.7% This suggests that regular hamstring stretching while taking part in a rigorous exercise programme will halve your risk of suffering a lower-leg injury.
Unfortunately, this study does not examine any other factors that could
contribute to injury risk, such as weight or rear-foot motion of the groups. It is possible that, as well as not stretching, there were more 'pronator' types in the control group, which could account for the increased injuries. However, while this study may not be perfect, it does give some scientific evidence that it is worthwhile developing hamstring flexibility during exercise programmes.
What is the connection between abdominal endurance, posture and lower back pain?
In this study (Mulhearn & George, 1999, Physiotherapy 85(4), pp 210-216) 22 gymnasts, along with 22 matched controls, were tested for abdominal muscle endurance and posture type, and these were compared with the lower back pain history of each subject. The aim of the study was to investigate any possible relationship between the three.
Abdominal muscle endurance was assessed by the length of time a specific exercise could be maintained, using a pressure biofeedback unit. Four exercises of increasing difficulty were tested, and in general, for both the gymnasts and controls, the holding time reduced as the exercise level went up. Postural type was assessed subjectively by observation, and categorised into 'lordotic', 'sway' or 'ideal'.
It was found that abdominal muscle endurance was lower in those with 'lordotic' posture,and in those with lower back pain. This suggests that the type of posture and/or the symptoms are related to a deconditioning of the abdominals. The researchers also found that the 'sway' posture was the most common and more highly related to lower back pain.
This study further supports the idea that abdominal muscle endurance, in particular the ability to hold a fixed position with stability, and correct posture, are related to lower back pain. This reinforces the inclusion of abdominal-strength exercises and re-education of posture in lower back pain treatment.