Limited inclusion of ethnically diverse and socioeconomically disadvantaged populations in pain research undermines external validity, generalizability, and equity. This comprehensive review synthesized evidence on effective strategies to recruit and retain these populations in pain studies. We searched Medline, Web of Science, Embase, Scopus, and CENTRAL (12 April 2025) and included studies in which ethnically diverse and socioeconomically disadvantaged participants comprised ≥75% of the sample. Quantitative data were pooled using random-effects meta-analyses of proportions, with prespecified subgroup analyses, and qualitative findings were integrated through thematic synthesis. Certainty of evidence was evaluated using GRADE. Eighteen studies (n = 4611; 11 experimental, 5 observational, 2 qualitative), primarily from the United States and involving chronic pain, met inclusion criteria. Overall enrollment among ethnically diverse and socioeconomically disadvantaged groups was 37% (95% CI 18–58%), with significantly higher enrollment in observational studies (84%, 95% CI 78–90%) than in experimental trials (22%, 95% CI 10–36%; p < 0.001). Overall retention was 77% (95% CI 64–88%) and did not differ significantly by study design. Statewide disease-clinic networks, purposive community-leader engagement, and snowball sampling produced the highest enrollment, whereas medical-record screening yielded the lowest enrollment but the highest retention. Compensation and reminder strategies were similarly effective for retention. Thematic synthesis highlighted trust, culturally and linguistically tailored communication, hybrid and flexible visit schedules, transportation assistance, and clinician engagement as key facilitators. GRADE certainty was low for enrollment and moderate for retention. Community-engaged recruitment strategies, clinician referrals, culturally tailored materials, hybrid procedures, and modest incentives can substantially improve participation of ethnically diverse and socioeconomically disadvantaged populations in pain research. Standardized CONSORT-style reporting of recruitment/retention flowcharts according to strategy and ethnicity/socioeconomic status is essential to refine evidence-based strategies in the future.

Objective Investigating the optimal interstimulus interval (ISI) and the 24-hour test-retest reliability for intrahemispheric dorsal premotor cortex (PMd) – primary motor cortex (M1) connectivity using dual-site transcranial magnetic stimulation (dsTMS). Methods In 21 right-handed adults, left intrahemispheric PMd–M1 connectivity has been investigated with a stacked-coil dsTMS setup (conditioning stimulus: 75% of resting motor threshold; test stimulus: eliciting MEPs of 1–1.5 mV) at ISIs of 3, 5–8, and 10 ms. Additionally, M1–M1 short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were investigated to assess comparability to standard paired-pulse setups. Results Conditioning PMd led to significant inhibition of M1 output at ISIs of 3 and 5 ms, whereas 10 ms resulted in facilitation (all, p < 0.001), with a fair test-retest reliability for 3 (ICC: 0.47) and 6 ms (ICC: 0.44) ISIs. Replication of SICI (p < 0.001) and ICF (p = 0.017) was successful, with excellent test-retest reliability for SICI (ICC: 0.81). Conclusion This dsTMS setup can probe the inhibitory and facilitatory PMd–M1 connections, as well as reliably replicate SICI and ICF paradigms. Significance The stacked-coil dsTMS setup for investigating intrahemispheric PMd–M1 connectivity offers promising possibilities to better understand motor control.