Related by context. Frequent words. (Click for all words.) 68 alertness 57 cognitive function 55 aerobic capacity 54 cognitive 53 cognitive functioning 53 libido 52 metabolism 52 bone density 52 cognitive functions 51 irritability 51 cognition 51 cognitive abilities 51 arousal 51 wakefulness 50 sleepiness 50 Melatonin 50 stamina 50 daytime sleepiness 50 endorphins 49 aerobic exercise 49 drowsiness 49 insulin sensitivity 49 exertion 48 strenuous exercise 48 caffeine 48 digestion 48 stress hormones 48 reflexes 47 metabolic 46 cortisol levels 46 fluid intake 46 Caffeine 46 B vitamins 46 mental faculties 46 dopamine 46 anti oxidant 46 electrolytes 46 physiological 46 norepinephrine 46 appetite suppressant 46 vitamin B6 46 caffeine intake 45 blood sugar 45 Sleep deprivation 45 physical exertion 45 ADHD symptoms 45 acetylcholine 45 satiety 45 endurance 45 hyperactivity 45 blood glucose levels 45 erections 45 cortisol 45 stimulant 45 melatonin 45 self esteem 45 cardio workout 44 tiredness 44 physiologically 44 REM sleep 44 serotonin 44 antioxidant 44 GABA 44 facial muscles 44 Vitamin E 44 aerobic 44 sexual arousal 44 anti oxidants 44 glucose metabolism 44 relaxation techniques 44 sleeplessness 44 relieve stress 44 lung function 43 muscles 43 stimulants 43 taurine 43 sociability 43 dexterity 43 thyroid function 43 thyroid hormone 43 stressful situations 43 Antidepressants 43 muscle cramps 43 willpower 43 mindfulness 43 Vitamin C 42 gait 42 CoQ# 42 drowsy 42 caloric intake 42 Dopamine 42 levodopa 42 eyesight 42 hydration 42 Hormone 42 lowering cholesterol 42 antioxidants 42 calmness 42 impulsivity 42 sleep 41 physiologic