Background Ergonomics risk assessment tools are vital for evaluating awkward postures in various industries, with a primary focus on biomechanical factors. However, existing observational techniques often fail to meet specific postural loading criteria or are inadequate to establish validity, especially in agricultural settings. Enhancements in these tools have been guided by extensive literature reviews. Objective This study aimed to develop a new assessment tool, the Agricultural Ergonomics Risk Assessment (AERA), by utilizing electromyography (EMG) to classify postural loads and prioritize risks. Method This paper describes an experimental study utilizing EMG to analyze postural loads, emphasizing biomechanical factors and including an evaluation of individual and occupational risk factors associated with musculoskeletal disorders (MSD). The validity and reliability of AERA were assessed by five experts and thirty evaluators. Results The study revealed strong effects of varying loads and postures on muscle activation. A key finding was the application of biomechanical factors to assess risk levels associated with awkward postures, especially regarding the prevalence of MSD in the neck, trunk, and arm regions. The evaluation indicated a Cronbach's alpha coefficient of 0.97 for precision in content validity of risk assessment criteria. Reliability tests comparing AERA with OWAS, RULA, and REBA yielded Cronbach's alpha coefficients of 0.99, 0.84, 0.93, and 0.88, respectively. Conclusion AERA's evaluation criteria incorporating specific and comprehensive risk factors produced the highest levels of test-retest reliability, making it a valuable screening tool for the agricultural sector.