Fatigue Susceptibility of the Lumbar Extensor Muscles among Smokers

Abstract

Background and Purpose Cigarette smoking is associated with poor physical fitness and muscle strength. These conditions are related to the development of mechanical low back pain. The specific effect of smoking on the characteristics of lumbar extensors has not previously been investigated. The objective of this study is to determine the isometric lumbar extensor strength, before and after fatigue challenge, among smokers and non-smokers. Methods A pre-test and post-test design was used to determine the differences in the lumbar extensor strength between smokers and non-smokers. Fifty-three male volunteers (29 smokers and 24 non-smokers) aged 21-47 years had their isometric lumbar extensor strength measured at seven spinal angles, from 72° to 0° of lumbar flexion, before and after fatigue challenge. Volitional muscle fatigue was induced by dynamic exercise with a load equal to 50% of the subject's peak torque on the pre-fatigue test. A composite fatigue index was then calculated. Descriptive statistics, analysis of covariance and multivariate analysis of variance were used. Results Smokers showed a significant reduction in strength both before and after fatigue challenge across all angles (p < 0.05). Smokers also showed a higher fatigue index than non-smokers (32% and 9.7%, respectively). The influences of age, body mass index and physical activity were negligible. Conclusions Strength deficit and fatigue susceptibility of the lumbar extensors among smokers may indicate that they are susceptible to back injuries, specifically after repetitive mechanical stress to the lumbar spine. Cigarette smoking is associated with poor physical fitness and muscle strength. These conditions are related to the development of mechanical low back pain. The specific effect of smoking on the characteristics of lumbar extensors has not previously been investigated. The objective of this study is to determine the isometric lumbar extensor strength, before and after fatigue challenge, among smokers and non-smokers. A pre-test and post-test design was used to determine the differences in the lumbar extensor strength between smokers and non-smokers. Fifty-three male volunteers (29 smokers and 24 non-smokers) aged 21-47 years had their isometric lumbar extensor strength measured at seven spinal angles, from 72° to 0° of lumbar flexion, before and after fatigue challenge. Volitional muscle fatigue was induced by dynamic exercise with a load equal to 50% of the subject's peak torque on the pre-fatigue test. A composite fatigue index was then calculated. Descriptive statistics, analysis of covariance and multivariate analysis of variance were used. Smokers showed a significant reduction in strength both before and after fatigue challenge across all angles (p < 0.05). Smokers also showed a higher fatigue index than non-smokers (32% and 9.7%, respectively). The influences of age, body mass index and physical activity were negligible. Strength deficit and fatigue susceptibility of the lumbar extensors among smokers may indicate that they are susceptible to back injuries, specifically after repetitive mechanical stress to the lumbar spine.