Endurance of trunk muscles in persons with chronic low back pain: assessment, performance, training

Trunk muscles are designed to fulfill their role of continuous activity throughout the day, but pain and inactivity alter muscles so that they fatigue in normal situations. Lack of endurance of the trunk muscles is an important factor in low back pain (LBP). This paper examines some methods to objectively test endurance of trunk flexor and extensor muscles in static and dynamic situations, and presents results of endurance testing in persons with chronic LBP compared to nonimpaired cohorts. Self perception of fitness affects some test results. Methods for increasing endurance are discussed along with benefits observed from training programs.

Distinguishable groups of musculoskeletal low back pain patients and asymptomatic control subjects based on physical measures of the NIOSH Low Back Atlas

STUDY DESIGN

The authors performed an empirical prospective study of 115 patients referred to physical therapy for low back pain and 112 control subjects of similar age and gender.

OBJECTIVES

The authors defined and compared subgroups based on physical tests and described demographic and psychosocial characteristics by group.

SUMMARY OF BACKGROUND DATA

Prospective studies of intervention for persons with low back pain are limited by inability to randomize subjects into distinguishable groups. Previous attempts have not been empirical and have not focused on musculoskeletal LBP.

METHODS

Ten physical therapists administered 52 tests and 6 questionnaires to subjects in seven different clinics. Data were subjected to reliability and cluster and comparative analyses.

RESULTS

Tests were reliable. Groups were distinguished by measures of symmetry, flexibility, strength, and dynamic mobility.

CONCLUSION

Distinguishable groups can be determined; decreased trunk mobility characterized all groups of patients and imbalances in muscle length, strength, and symmetry described specific groups of subjects with and without low back pain.

Endurance training of trunk extensor muscles

BACKGROUND AND PURPOSE

The purpose of this study was to assess the effects of an endurance exercise protocol on the isometric holding time of the trunk extensor muscles (mechanical fatigue measure) and on the recorded median frequency (MF) measurements from the surface electromyogram (physiological fatigue measure).

SUBJECTS

Twenty-eight healthy female volunteers were selected to participate in the study.

METHODS

The subjects were stratified by activity level and then assigned to an exercise or a control group and tested at weeks 0, 3, and 6. Reliability (r) of the measurements, established by testing each subject twice at week 0, was .87. Exercise group subjects trained at home twice daily for 6 weeks, progressing by established protocol.

RESULTS

The exercise group subjects increased their isometric holding time by 22% after 6 weeks. The control group showed no significant changes.

CONCLUSION AND DISCUSSION

The home program was believed to be effective for increasing isometric endurance of the trunk extensors, measured by holding time. The MF measurements prior to and just after a fatiguing contraction remained stable over time. The change in the slope of the MF with fatigue did not reach statistical significance. This physiologic measure of fatigue did not show commensurate changes with training in this group of subjects. Possible reasons for the results are discussed.

The power struggle: definition and evaluation of power of muscular performance

The authors define five different measurements of power of muscular performance. Using an isokinetic dynamometer, the velocity of motion is constant and thus can be controlled. Power, therefore, can be readily assessed. The speed of muscular contraction is of physiological and functional interest. The time it takes for muscles to develop force, the rate at which muscles can contract and sustain a force throughout the range of motion, and the relationship of speed to force are all facets of power. At least five terms which connote power of muscular performances are used today. These terms are power, peak power, average power, instantaneous power, and contractile power. The current misunderstanding of the terms and their misuses are discussed. Suggestions are offered for circumventing confusion in using power to describe motor performance.