Fiber Typing of the Erector Spinae and Multifidus Muscles in Healthy Controls and Back Pain Patients: A Systematic Literature Review.

OBJECTIVE: Understanding the changes in muscle fiber typing is relevant in the context of muscle disorders because it provides information on the metabolic profile and functional capacity. The aim of this study was to systematically review the literature comparing muscle fiber typing in the back muscles of healthy subjects with low back pain (LBP) patients. METHODS: Predefined keywords regarding muscle fiber typing and back muscles were combined in PubMed and Web of Science electronic search engines from inception to August 2014. Full-text articles were independently screened by 2 independent, blinded researchers. Full texts fulfilling the predefined inclusion criteria were assessed on risk of bias by 2 independent researchers, and relative data were extracted. Data were not pooled because of heterogeneity in biopsy locations and population. RESULTS: From the 214 articles that were identified, 18 met the inclusion criteria. These articles evaluated the muscle fiber type distribution or proportional fiber type area between muscles, muscle layers, men, and women or healthy subjects and LBP patients. Regarding muscle fiber type distribution, findings in healthy subjects and LBP patients show no or inconclusive evidence for intermuscular and interindividual differentiation. Studies evaluating the proportional fiber type area also suggest little intermuscular differentiation but provide plausible evidence that the proportional area occupied by type I fibers is higher in women compared to men. The evidence for differentiation based on the presence of low back pain is conflicting. CONCLUSION: This study found that the evidence regarding muscle fiber typing in back muscles is either inconclusive or shows little differences. The most plausible evidence exists for differentiation in proportional fiber type area depending on sex.

Acromiohumeral distance and 3-dimensional scapular position change after overhead muscle fatigue.

CONTEXT: Muscle fatigue due to repetitive and prolonged overhead sports activity is considered an important factor contributing to impingement-related rotator cuff pathologic conditions in overhead athletes. The evidence on scapular and glenohumeral kinematic changes after fatigue is contradicting and prohibits conclusions about how shoulder muscle fatigue affects acromiohumeral distance. OBJECTIVE: To investigate the effect of a fatigue protocol resembling overhead sports activity on acromiohumeral distance and 3-dimensional scapular position in overhead athletes. DESIGN: Cross-sectional study. SETTING: Institutional laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 29 healthy recreational overhead athletes (14 men, 15 women; age = 22.23 ± 2.82 years, height = 178.3 ± 7.8 cm, mass = 71.6 ± 9.5 kg). INTERVENTION(S): The athletes were tested before and after a shoulder muscle-fatiguing protocol. MAIN OUTCOME MEASURE(S): Acromiohumeral distance was measured using ultrasound, and scapular position was determined with an electromagnetic motion-tracking system. Both measurements were performed at 3 elevation positions (0°, 45°, and 60° of abduction). We used a 3-factor mixed model for data analysis. RESULTS: After fatigue, the acromiohumeral distance increased when the upper extremity was actively positioned at 45° (Δ = 0.78 ± 0.24 mm, P = .002) or 60° (Δ = 0.58 ± 0.23 mm, P = .02) of abduction. Scapular position changed after fatigue to a more externally rotated position at 45° (Δ = 4.97° ± 1.13°, P < .001) and 60° (Δ = 4.61° ± 1.90°, P = .001) of abduction, a more upwardly rotated position at 45° (Δ = 6.10° ± 1.30°, P < .001) and 60° (Δ = 7.20° ± 1.65°, P < .001) of abduction, and a more posteriorly tilted position at 0°, 45°, and 60° of abduction (Δ = 1.98° ± 0.41°, P < .001). CONCLUSIONS: After a fatiguing protocol, we found changes in acromiohumeral distance and scapular position that corresponded with an impingement-sparing situation.

Sonographic evaluation of the acromiohumeral distance in elite and recreational female overhead athletes.

OBJECTIVE: To compare the acromiohumeral distance (AHD) and the change of this distance during abduction between the dominant and nondominant shoulders of female overhead athletes and to compare AHD between elite and recreational female athletes. DESIGN: : Case-control study. SETTING: Laboratory, institutional. INDEPENDENT VARIABLES: "Side" (dominant and nondominant), "group" (elite and recreational athletes), and "degree of abduction" (0, 45, and 60 degrees). PARTICIPANTS: Sixty-two female overhead athletes participated in this study: 29 elite handball players and 33 recreational overhead athletes of different sports disciplines (volleyball, water polo, squash, and badminton). MAIN OUTCOME MEASURES: Acromiohumeral distance was measured at 3 positions of abduction using ultrasound: at 0, 45, and 60 degrees of abduction. RESULTS: Acromiohumeral distance measurements showed good test-retest reliability (intraclass correlation coefficients between 0.88 and 0.92). In all overhead athletes, the AHD was significantly larger on the dominant side compared with the nondominant side, at all positions of abduction (mean difference = 0.94 ± 0.18 mm). Significant reduction of the AHD during abduction occurred relative to the initial size at 0 degree of abduction, at both sides. When comparing elite and recreational athletes, the AHD was significantly larger in elite athletes (mean difference = 0.92 ± 0.47 mm). Moreover, significantly less reduction occurred during the first degrees of abduction (0-45 degrees) in elite athletes (9.37% ± 2.17% reduction) compared with the recreational athletes (17.68% ± 2.03% reduction). CONCLUSIONS: The AHD is larger on the dominant side compared with the nondominant side and in elite female athletes compared with recreational female athletes. Moreover, less reduction of the AHD occurs in the elite athlete group during the first 45 degrees of abduction.