We aimed to examine to what extent a lateral infraclavicular brachial plexus block affected the axillary and the suprascapular nerve. We included patients undergoing hand surgery anaesthetised with a lateral infraclavicular brachial plexus block. Our primary outcome was the relative change in surface electromyography during maximum voluntary isometric contraction of the medial deltoid muscle (axillary nerve) and the infraspinatus muscle (suprascapular nerve) from baseline to 30 min after the block procedure. A reduction in electromyography of > 50% defined a successful block. The impact of the block on the shoulder nerves was compared with the surgical target nerves of the arm and hand (musculocutaneous, radial, median and ulnar nerves). Twenty patients were included. The medians of the relative changes in the surface electromyography were significantly reduced (both p < 0.001) with 92% for the deltoid muscle and 30% for the infraspinatus muscle, respectively. In total, 18 out of 20 patients had reductions > 50% for the deltoid muscle, which was significantly different from the infraspinatus muscle, where the proportion was 5 out of 20 (p < 0.001). The medians of the relative reductions in electromyography for the arm and hand muscles were 90-96%, similar to the effect on the deltoid muscle. Our results suggest that a lateral infraclavicular block provides block of the axillary nerve comparable to the block of the surgical target nerves. The suprascapular nerve is blocked to a lesser degree. Combining a lateral infraclavicular brachial plexus block with a selective suprascapular block for shoulder surgery warrants further studies.