INTRODUCTION: Posterior shoulder musculature play a crucial role in rehabilitation of shoulder pathology. PURPOSE: To determine which type of posterior shoulder muscular endurance protocol, endurance repetitions or endurance with static isometric holds, improves muscular endurance more. Poor posterior shoulder endurance can be a precursor to shoulder injury. METHODS: Healthy participants were divided into three groups; control, repetition training, and an isometric training group. The training groups performed shoulder strengthening exercises 2-3x/week for 10 weeks. Both groups were advised to exercise at level of 4-6 on the Omni- Resistance Scale. Control group didn't exercise. Strength and endurance testing was at baseline, 5, and 10 weeks. Strength was measured via manual muscle testing (MMT) with a handheld digital dynamometer (HDD). Endurance testing included a side-lying external rotation repetitions test and side-lying external rotation (ER) isometric hold. The dominant (DOM) shoulder was used for all strengthening. RESULTS: No difference was found between DOM and non-dominant (ND) shoulder flexion (F(10,350)=1.72, p=0.075), abduction (F(10,350)=1.56, p = 0.117), or ER (F(10,350) = 1.22, p= 0.277) strength between the three training groups over time. No difference was found between DOM and ND shoulder ER isometric endurance test between groups over time (F(10,350) = 1.04, p=0.407). A difference was found between DOM and ND ER endurance repetition test between groups over time (F(10,350)= 2.69, p=0.004). CONCLUSION: While each group saw improvements in shoulder strength, neither training groups produced a significant increase in strength compared to the control. However, shoulder ER repetition endurance was improved in both training groups.