I was skeptical about this product since the market has been going down the drain and not what it used to be, like the good old glorious days in the house of pain and gain.I started working a lot a few months ago, along with cardio and body weight exercises, trying to get ready for Boot Camp, and my legs would feel weak at times, have some low energy as well, and get super sore afterwards.I took this their product, and not only did I feel energized, I performed great on my first run with this MK, and the exercises were amazing. I was like the energizer bunny, just going and going.The next two days, I only felt some minor soreness on my abs but nothing major, and my legs were ok.I did not feel any jitter and no negative side effects such as nausea, stomach problems, or anything else, as you would with some fat burners or pre-workouts.I did take this product around 8 PM, and by midnight I was still out exercising in 98 degree weather (I live in the desert. it’s hot out at night). I do recommend taking this MK earlier in the day or morning. Once I went to bed, my sleep was very light, and I couldn’t go into a deep sleep since I took the pills a bit late. Very recommended!! I I'll give you 5 star rating