EE reported pulling a muscle in EE's left upper arm on 05DEC21 while removing a tail pulley guard. Incident was initially a first aid only/ no medical case. On 21DEC21 EE requested medical evaluation because EE's arm still hurt. EE was medically evaluated and diagnosed with a strain of the left deltoid muscle. EE was prescribed P/T and released to work with restrictions on 21DEC21.