In this study the photoplethysmography (PPG) signals while mental workload during resting state and physical fatigue and tiredness are investigated. The aim is to examine the relationship between restricted physical fatigue and mental workload, and effects of mental workload on PPG during pre- and post- exercise accompanied with mathematical exercise besides physiological and electrophysiological measurements like aerobic capacity (VO2max) the so-called cardiorespiratoire endurance criterion, oxygen consumption, heart rate, electrocardiograph (ECG), electroencephalography (EEG) gained in our previous research. In this study, differences between PPG signals between two discrete groups namely elite and amateur athlete groups are investigated in detail. Variances of PPG signals are analyzed and discussed within and between groups. Results specify that variances in PPG of elite group are less than variances in amateur group's PPG data, and also it's been observed that PPG signals within group may vary like in our elite group.