Abstract

This paper is aimed to establish whether stretching techniques, as they affect the soft tissues of the lower back, are conducive to promoting or damaging its health and efficiency. The criterion employed was to examine whether postures, exercises and techniques involving stretching the soft tissues of the lumbar region assisted or hampered the lower back in functioning efficiently as a loco-motor system without undue discomfort. Particular attention was given to studies and articles concerned with the potential for stretching exercises to cause or rehabilitate mechanical low back pain. Searches were conducted for reports of studies on the effects of stretching soft tissues generally and those of the low back in particular. Reports of random controlled trials relating stretching to relief or inducement of lower back pain were of primary concern. This report reviews only pertinent trials and studies that the meta reviews considered to be of good quality.

Little scientific evidence or consensus was found on what constitutes safe and effective stretching and the value of stretching in preventative and remedial back care, but there were few reported trials specific to the question. There appears to be little quantitative data to support the claim that trunk flexibility improves back health or reduces the risk of injury and has little predictive value for future back trouble.

KEYWORDS: Low back pain, stretching, safety, effectiveness

Introduction

The perceived value of stretching and the techniques employed derive mostly from empirical evidence and historical precedent but its value remains unclear (British Medical Journal Editorial 2002). There are acute and chronic adaptations to stretching soft tissue. These can include reducing passive muscular tension, altered posture and changes in the molecular tissue structure. These events may increase or reduce pain, tissue strength and spinal stability, the outcome dependent on the initial qualities of the tissue and the appropriateness of the stretching technique (Alter 1996). Although there is an absence of a defined clinical assessment of what constitutes sufficient mobility no reported case studies of persons sustaining injury to the low back by performing stretching exercises were found in the course of this research.

Stretching, in the context of this paper, is static stretching whereby soft tissue is elongated and held for at least a few seconds. It may be active whereby antagonist muscles provides sufficient force to lengthen the muscle, or passive whereby gravity, another person or another part of the body provides the force. Stretching soft tissue may also result from oscillatory movements imposed under spinal mobilization and manipulation. Stretching exercises may be employed in the rehabilitation of structural damage and dysfunction although this is subject to conjecture. Its role in enhancing spinal stability is less certain and subject to interpretations on its impact on muscle contractile force. McKenzie (1981) extension exercises and Williams (1937a; 1937b; 1955 all cited in Elnagger 1991; Nwuga et al 1985) flexion exercises have the rare accolade of scientific support for their selective use in treating mechanical back pain.

Inadequate flexibility in soft tissues limits range of joint movement that may impair performance through tension, muscular imbalance and pain. This may be due to acute muscular tension that mild stretching can alleviate without inducing structural changes in the tissues. The overall results from the literature suggest that stretching might be useful as part of a rehabilitation process but not as a priority to be used in isolation to treat mechanical back pain. The consensus appeared to be that soft tissues should initially be strengthened to enable them to withstand forces imposed on them by stretching (Waddell 1998, Coulter 2000). Good quality controlled trials would be useful to clarify the efficacy of stretching but the contribution of specific exercises will be difficult to separate from the overall effects where other interventions are used. In the meantime, the efficacy of stretching can be inferred from knowledge of the impact of tensile forces on soft tissues combined with observation and informed interpretation of the sensory feedback.

Methodology

Searches were conducted for reports of studies on the effects of stretching soft tissues generally and those of the low back in particular. Reports of random controlled trials relating stretching to relief or inducement of lower back pain were of primary concern. Reports on the effects of stretching on injury prevention and athletic performance were also considered.

a. References to respective trails and studies were derived from published meta reviews. This report reviews only pertinent trials and studies that the meta reviews considered to be of good quality.

b. Texts on the biomechanics of the low back and the biomechanics of stretching soft tissues were sought from major contemporary authors.

c. Texts were sought describing the practices of stretching tissues of the low back used by manual therapists and fitness, yoga and pilates instructors.

Literature searches were conducted on the British Library catalogue and the internet using Medline, Pubmed, Science Direct, BMJ.com and other search engines.

Clinical evidence of the effects of stretching:

There is little direct evidence to establish links between stretching the low back and pain reduction or other improvements in efficiency. Most surveys and trials were heterogeneous covering numerous interventions making it difficult to isolate any effects of stretching. The largest survey of articles and studies concerned with the treatment modalities for low back pain was conducted by the U.S. Agency for Health Care Policy and Research, 1994 (cited in Nachemson and Jonsson 2000) and has been updated and incorporated into later reviews (Waddelll 1998; van Tulder et al 2003). Twenty-eight random controlled trials reviewing the effects of specific back exercises, including flexion, extension and stretching were identified by Waddell from which only two were considered to be of high quality. There appears to be no evidence of clinical effectiveness for any specific exercise or exercise therapy in treating acute low back pain, i.e. of less than twelve weeks duration. However, there is some strong evidence of exercise therapy being effective in treating chronic low back pain, i.e. of more than twelve weeks duration (van Tulder et al 2003).

Earlier meta analysis include Faas (1996) who updated a survey by Koes et al (1991). Neither found any substantial evidence that specific back exercises provide clinically significant improvements in acute lower back pain and that the type of exercise employed made little difference to the outcome of rehabilitation. A meta-analysis by Evans and Richards (1996) concluded exercise programmes did relieve pain and improve function in patients with chronic lower back pain, although the exercises were not exclusively stretching. An earlier project by the Quebec Task Force (1987) reviewed the rehabilitation of chronic low back pain and similarly concluded there was little evidence to support any particular rehabilitation programme.

Individual surveys of note include Deyo et al (1990) who, in an otherwise controlled study, reported that patients with chronic back pain improved after four weeks of flexibility training but this was also combined with using transcutaneous electrial nerve stimulation (TENS). Studies examining spinal flexibility in the context of back pain reported mixed findings but all generally agreed measurers of flexibility are a poor predictor of back problems (Biering and Sorensen 1984; Battie et al 1986; Troup et al 1987). Furthermore, hip and trunk flexibility was found to be disadvantageous in the economy of walking (Gleim et al 1990), jogging (Gleim and McHugh 1997) and in running (Craib et al.1996) possibly because increased stiffness might be associated with increased muscle energy storage (Gleim and McHugh 1997). These authors concluded that flexibility is important for performances in sports that rely on extreme ranges of movement, but that decreased flexibility may increase economy of movement in sports using only the mid range of movement.

Shrier (1999) identified twelve controlled trials relating stretching before exercise to injury rates and concluded that the only studies showing beneficial effects included other interventions. Studies focusing on stretching alone actually found increases in injury rates. This included a study of elite female rowers who performed specific stretches for the low back (Howell 1984). This found high correlations between hyperflexion of the lumbar spine and incidence of low back pain and adherence to a regular stretching programme and incidence of low back pain. The stretching programme was self directed and unspecified and it was not clear whether these athletes became injured because of stretching or stretched because they were injured. However, there was no correlation between hypermobility in the lumber spine and muscle weakness compared to the rowers with a normal or hypomobile lumbar spine. A meta analysis by Herbert and Gabriel (2002) focused on stretching limbs before or after exercise found it does not prevent delayed onset muscle soreness.

The only exercises incorporating stretching to be identified with a positive effect on back pain were spinal flexion exercises advocated by Williams (1937a;1937b:1955 all cited in Elnagger 1991) and spinal extension exercises advocated by McKenzie (1981). These featured in a number of studies but Elnagger et al (1991) was identified consistently in meta surveys as being of high quality and was the only study focusing exclusively on stretching techniques to obtain a positive result. It

Figs 1 (left) and 2: Spinal flexion from sitting upright.

Figs 3 (left) and 4. Spinal flexion in sitting and squatting from standing.

Fig 5 (left) Spinal flexion from supine fig 6 (above); fig 7 (below)

Figs 1 to 7 illustrate the final postural positions achieved in Williams flexion exercises described in Elnagger et al 1991.

Figs 8 to 11 (below) illustrate the McKenzie back extension exercises described by Elnagger et al 1991

Fig 8 (above); fig 10 (below) Fig 9 (above); Fig 11 (below)

investigated the effects of the respective flexion and extension exercises on low back pain and spinal mobility in two respective groups of patients with chronic mechanical low back pain. Both groups reported equal reductions in back pain severity but only those performing the flexion exercises reported improved saggital mobility. Neither group recorded an improvement in coronal or transverse mobility of the thoracolumbar spine. Nwuga et al (1985) made an earlier study of the effects of the respective Williams and McKenzie protocols and their effects on back pain and on mobility in three dimensions. Their study was confined to subjects suffering low back pain caused by a prolapsed disc although they used the same procedure as Elnagger et al (1991) of confining groups exclusively to one exercise regime. Those performing extension exercises had more reduction in pain, improved mobility, a more rapid response and less relapse.

A number of the trials found correlations between exercise and relief of chronic back pain. (Report of International Paris Task Force 2000; Friedrich et al 1998, both cited in ACSM 2002, p133). Manniche et al (1991) found a significant correlation between back strengthening exercise and relief of chronic back pain. A back extension exercise similar to that in Fig 10 was a major component used in this study. The exercise involves repeated back extension movements by active muscle contraction. They did not measure the effects of individual exercises on back pain or the effects of exercises on specific muscles so the respective contributions are not known.

Lack of specific evidence of the effects of any particular exercise has lead some commentators to conclude that exercise of any kind which does not stress the low back unduly is of value. Indeed, some advocate that the exercise should be of a tough nature to install the patient with a degree of confidence in the structural capabilities of their backs (Frost et al 1998). This is linked to speculation of a ‘psycho-social’ contribution to back pain (Waddell 1998).

Key Points:

Lack of specific evidence of the effects of any particular exercise has led some commentators to conclude that exercise of almost any kind which does not stress the low back unduly is of value
There appears to be no evidence of clinical effectiveness for any specific exercise or exercise therapy in treating acute low back pain, i.e. of less than twelve weeks duration. However, there is some strong evidence of exercise therapy being effective in treating chronic low back pain, i.e. of more than twelve weeks duration (van Tulder et al 2003).
Exercise programmes did relieve pain and improve function in patients with chronic LBP, although the exercises were not exclusively stretching.
Flexibility training combined with using transcutaneous electrial nerve stimulation appears beneficial and there is some evidence to suggest stretching alone might actually increases injury rates.
The only exercises incorporating stretching to be identified with a positive effect on back pain were spinal flexion exercises advocated by Williams (1937a;1937b:1955 all cited in Elnagger 1991) and spinal extension exercises advocated by McKenzie (1981). Those performing extension exercises have been found to have more reduction in pain, improved mobility, a more rapid response and less relapse.
Manniche et al (1991) found a significant correlation between back strengthening exercises, including lumbar extensions, and relief of chronic back pain.

Conclusion

Random controlled trials surveyed offered very little clinical evidence of either the benefits or injurious potential of stretching soft tissue in the context of therapy or exercise. Few random controlled trials solely concerned with stretching have been conducted. Those that attempt to measure the effects of stretching invariably include other interventions. Even fewer concern themselves exclusively with the lumbar spine. Moreover, there appears to be little scientific evidence to support claims that exercises to increase or maintain spinal range of motion succeeded in preventing lower back problems. The paucity of research evidence suggests that stretching soft tissues is based on historical precedent, custom and practice. It has been argued that flexibility and range of motion may not be particularly relevant to the health and efficiency of the low back. Conversely, there are no trials attempting to link the process of stretching the soft tissues of the low back with the inducement of injury.

There are continuing projects developing theoretical constructs based on both in vitro and in vivo studies to determine degrees of force required to exercise or to damage tissue (McGill 2002) but the results are not easily extrapolated to the stretching practices under discussion. In vitro studies have the serious restriction of being unable to observe living tissue in its natural context and tissue may behave somewhat differently in vivo. Difficulties with in vivo studies concern the inability to monitor the effects of a given force on soft tissues in isolation from other activities. Waddell (1998) cites the limitations of current biomechanical knowledge mostly induced from laboratory studies on cadavers limited to one or two motion segments of the spine and on ‘one or two specimens only’ (p140). The tissues are not metabolically active and cannot depict inflammation or healing. The spine tested to failure in the laboratory offers little information about the causes of backache (Waddell 1998).