An attempt has been made to analyse the progression of muscle fatigue using mean power ratios (MPRs) derived from B-distribution time-frequency spectrum of surface electromyography signals. For this purpose, signals are recorded from the biceps brachii muscle of 30 healthy adult volunteers. Fifteen subjects carried out isometric contractions and the rest performed dynamic muscle contractions until task failure. The signals are preprocessed and subjected to B-distribution-based time-frequency analysis. Subsequently, the MPR of medium-to-low-frequency band (M/LFB) and high-to-LFB (H/LFB) are extracted from the time-frequency spectrum. Furthermore, the slope is calculated using the linear regression technique. Results show that MPR of M/LFB and H/LFB exhibit a decreasing trend during the progression of muscle fatigue condition. The strength of the peaks present in MPR of M/LFB progressively reduces and approaches zero at task failure for all subjects. Additionally, higher slope values are found in MPR of M/LFB in comparison with H/LFB. It appears that MPR of M/LFB is more sensitive for muscle fatigue analysis and may be used as an index for real-time monitoring in work place. © The Institution of Engineering and Technology 2016.