To understand the factors that determines human perception of effort. This study investigated the relationship between objective measures of exertion (handgrip force and electromyography – EMG) and perceived effort (Borg scale) during localized activities of the forearm muscles. This relation is important for understanding the factors that determine human perception of effort. Method: Two hand-gesture experiments (low effort) and one handgrip force experiment (moderate to high effort) were carried out. During the experiments, Borg ratings, grip forces and EMG signals from six forearm muscles were obtained. The relationship between objective measurements and perceived effort were investigated using generalized linear mixed models. Results: The linear models for predicting the Borg ratings based on gender and EMG provided R-squared values of up to 0.5 for generic models and up to 0.85 when fitting a model to individual subjects. In addition, the model based on the average EMG of all recorded muscles was found to as good as a model based on individual muscles. The results indicated that women rated low-effort activities as less being effortful than men, while there was no difference between genders for moderate- to high-effort activity. Conclusion: The findings of this study demonstrated that muscle activation level (i.e. EMG) is related to perceived effort for localized hand effort tasks and can explain a large part of an individual’s perceived effort. The results suggest that the perception of effort is related to the overall effort of the muscles and not to a specific muscle.