Work-related musculoskeletal disorders (WMSDs) are disorders of muscles, bones, joints, cartilage, tendons, and ligaments. These disorders are caused by overexertion, excessive load, vibration, etc. These factors lead to excessive muscle fatigue accumulation, hence WMSDs. Appropriate work design is needed to minimize or prevent these risks and provide sufficient rest periods to avoid muscle fatigue accumulation. While previous studies have shown that various tasks and industry activities lead to muscle fatigue, there is a notable gap in studies on the effect of rest intervals on muscle fatigue recovery time. Frequent rest breaks allow workers to recover and reduce the risk of WMSDs due to fatigue accumulation. However, taking overly extended breaks will most likely result in work disruption and loss of workers' performance. Accurate appropriation of rest intervals will solve this problem of muscle fatigue accumulation. This study developed a mathematical model to predict the muscle fatigue recovery time for a manual material handling (MMH) task using task characteristics – weight, duration, distance, frequency, and angle of lift – and drilling operation using drilling parameters – feed force, duration, drill bit diameter, and material hardness. The results show that the weight (p=0.0024) and duration (p=0.0131) significantly impacted the recovery time for the MMH task, while the feed force (p=<.0001), duration (p<.0001), and material hardness (p=0.0052), affected the drilling operation. The ANOVA show no significant difference between the actual and model-generated results for both studies. This study may be used for work design during MMH tasks and drilling operations to ensure muscle fatigue recovery.