Sex differences in strength at the shoulder: a systematic review

Abstract

Background: Understanding differential strength capability between sexes is critical in ergonomics and task design. Variations in study designs and outcome measures generates challenges in establishing workplace guidelines for strength requirements to minimize upper extremity risk for workers. The purpose of this systematic review was to collate and summarize sex differences in strength at the shoulder across movement directions and contraction types.

Methods: A total of 3,294 articles were screened from four databases (Embase, Medline, SCOPUS, and Web of Science). Eligibility criteria included observational studies, direct measurement of muscular joint, and healthy adult participants (18-65 years old). Strength outcome measures were normalized to percentages of male outputs to allow comparisons across articles.

Results: A total of 63 studies were included within the final review. Majority of articles observed increased strength in males; the gap between male-female strength was greater in flexion and internal/external rotation, with females generating ~30% of male strength; scaption strength ratios were most consistent of the movement groups, with females generating 55-62% of male strength.

Conclusion: Sex strength differences should be considered as an important factor for workplace task design as women are more at risk for occupational-related injuries than men in equivalent strength requirements. Differences in strength were not synonymous across motions; females demonstrated increased disparity relative to male strength in horizontal flexion/extension, forward flexion and internal/external rotation. Some movements had an extremely limited pool of available studies for examination which identified critical research gaps within the literature. Collating and quantifying strength differences is critical for effective workstation design with a range of users to mitigate potential overexertion risk and musculoskeletal injury.

Keywords: Biomechanics; Ergonomics; Isokinetic; Isometric; Shoulder; Strength differences/sex.

Figure 1. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart describing the screening process and inclusion of eligible articles for this review.

Figure 2. Representative motions for the nine shoulder planar movements included in the review.

Figure 3. Representative outcome ranges for shoulder articulations included in this systematic review.

Figure 4. Sex strength differences of abduction (left) and adduction (right).

Female strength metrics ranging from (A) 29–127% and (B) 43–107% of male strength, respectively. Articles in this review demonstrate that female strength centralized at ~40–80% (abduction) and ~45–65% (adduction) of male strength.

Figure 5. Sex strength differences of scaption.

Female strength metrics ranging from 55–62% of male strength.

Figure 6. Sex strength differences of flexion (left) and extension (right).

Female strength metrics ranging from (A) 33–107% and (B) 38–113% of male strength, respectively. Articles in this review demonstrate that female strength centralized at ~40–70% (flexion) and ~40–60% (extension) of male strength.

Figure 7. Sex strength differences of horizontal flexion (left) and horizontal extension (right).

Female strength metrics ranging from (A) 36–104% and (B) 36–97% of male strength, respectively. Articles in this review demonstrate that female strength centralized at ~40–55% (horizontal flexion) and ~40–50% (horizontal extension) of male strength.

Figure 8. Sex strength differences of internal rotation (left) and external rotation (right).

Female strength metrics ranging from (A) 32–105% and (B) 28–103% of male strength, respectively. Articles in this review demonstrate that female strength centralized at ~40–70% (internal rotation) and ~45–80% (external rotation) of male strength.