Isometric non-machine-based prevention training program: effects on the cross-sectional area of the paravertebral muscles on magnetic resonance imaging

Correlation between the fatty infiltration of paraspinal muscles and disc degeneration and the underlying mechanism

Background

Low back pain (LBP) is associated with lumbar disc degeneration (LDD) and fatty infiltration of paraspinal muscles. However, there are some controversies about the relationship between LDD and fatty infiltration of paraspinal muscles, and the causation of them is also not clear. Thus, we investigated whether the degree of LDD was associated with fatty infiltration of paraspinal muscles and preliminarily explored the underlying mechanism.

Methods

A retrospective study was conducted on 109 patients with chronic LBP. The degree of LDD was assessed by the Pfirrmann classification. Total muscle cross-sectional area, L4 vertebral body endplate area, and fat cross-sectional area at axial T2-weighted MRI were measured. Multifidus and lumbar disc specimens were taken from eight individuals undergoing discectomy for disc herniation. Gene and protein expression levels of TNF were quantified through qPCR assays and ELISA, respectively.

Results

The relative cross-sectional area, total muscle cross-sectional area, and muscle cross-sectional area asymmetry were not related to LDD. Pfirrmann grades correlated strongly with fatty infiltration of the multifidus and moderately with fatty infiltration of the erector spinae and the psoas muscles. Linear regression analysis suggested that Pfirrmann grades were most associated with fatty infiltration of the multifidus. Compared with II-degree degeneration discs (mild-degeneration group), fatty infiltration of the multifidus in IV-degree degeneration discs (severe-degeneration group) significantly increased, accompanied by increased mRNA expression of TNF. Meanwhile, the protein expression levels of TNF (pg/g protein) in discs (16.62 ± 4.33) and multifidus (13.10 ± 2.76) of the severe-degeneration group were higher than those in the mild-degeneration group (disc: 9.75 ± 2.18; multifidus: 7.84 ± 2.43). However, the mRNA expression of TNF in the multifidus was not significantly different between the two groups.

Conclusions

The results suggest that LDD is associated with fatty infiltration of the multifidus. The possible underlying mechanism is that LDD induces fatty infiltration by inflammation. Furthermore, compared with the erector spinae and the psoas muscles, fatty infiltration of the multifidus shows an optimal correlation with LDD, which may contribute to further understanding of LDD pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05466-8.

The effect of exercise training on lower trunk muscle morphology

BACKGROUND

Skeletal muscle plays an important role in maintaining the stability of the lumbar region. However, there is conflicting evidence regarding the effects of exercise on trunk muscle morphology.

OBJECTIVE

To systematically review the literature on the effects of exercise training on lower trunk muscle morphology to determine the comparative effectiveness of different exercise interventions.

DATA SOURCE AND STUDY SELECTION

A systematic search strategy was conducted in the following databases: PubMed, SportDiscus, CINAHL, the Cochrane Library and PEDro. We included full, peer-reviewed, prospective longitudinal studies, including randomized controlled trials and single-group designs, such as pre- to post-intervention and crossover studies, reporting on the effect of exercise training on trunk muscle morphology.

STUDY APPRAISAL AND SYNTHESIS

Study quality was assessed with the Cochrane risk-of-bias tool. We classified each exercise intervention into four categories, based on the primary exercise approach: motor control, machine-based resistance, non-machine-based resistance or cardiovascular. Treatment effects were estimated using within-group standardized mean differences (SMDs).

RESULTS

The systematic search identified 1,911 studies; of which 29 met our selection criteria: motor control (n = 12), machine-based resistance (n = 10), non-machine-based resistance (n = 5) and cardiovascular (n = 2). Fourteen studies (48 %) reported an increase in trunk muscle size following exercise training. Among positive trials, the largest effects were reported by studies testing combined motor control and non-machine-based resistance exercise (SMD [95 % CI] = 0.66 [0.06 to 1.27] to 3.39 [2.80 to 3.98]) and machine-based resistance exercise programmes (SMD [95 % CI] = 0.52 [0.01 to 1.03] to 1.79 [0.87 to 2.72]). Most studies investigating the effects of non-machine-based resistance exercise reported no change in trunk muscle morphology, with one study reporting a medium effect on trunk muscle size (SMD [95 % CI] = 0.60 [0.03 to 1.16]). Cardiovascular exercise interventions demonstrated no effect on trunk muscle morphology (SMD [95 % CI] = -0.16 [-1.14 to 0.81] to 0.09 [-0.83 to 1.01]).

LIMITATIONS

We excluded studies published in languages other than English, and therefore it is possible that the results of relevant studies are not represented in this review. There was large clinical heterogeneity between the included studies, which prevented data synthesis. Among the studies included in this review, common sources of potential bias were random sequence generation, allocation concealment and blinding. Finally, the details of the exercise parameters were poorly reported in most studies.

CONCLUSION

Approximately half of the included studies reported an increase in lower trunk muscle size following participation in an exercise programme. Among positive trials, studies involving motor control exercises combined with non-machine-based resistance exercise, as well as machine-based resistance exercises, demonstrated medium to large effects on trunk muscle size. Most studies examining the effect of non-machine-based resistance exercise and all studies investigating cardiovascular exercise reported no effect on trunk muscle morphology. However, these results should be interpreted with caution because of the substantial risk of bias and suboptimal reporting of exercise details in the included studies. Additional research, using methods ensuring a low risk of bias, are required to further elucidate the effects of exercise on trunk muscle morphology.