The eyes of the participants were closed and the VFP goggles illuminated in alternative manner; first the right eye, then the left. The rate at which the photic stimulation was conducted ranged between 0.5 Hz and 50 Hz. Of the 50 patients with migraines, 49 considered their headache as having been “helped” by the stimulation and 36 noted that their headache had completely “stopped” from the VFP goggles.
Quick example: Brainwave readings (with an EEG machine) have shown that brainwaves of 2Hz occur when an individual is asleep. Scientists can create special audio recordings, which contain an encoded 2Hz frequency. While listening to such audio, the brain naturally follows (entrains) toward that 2Hz frequency, lowering its brainwave patterns. That's "brainwave entrainment." The net result is that when listening to such an audio recording, you (the listener) will naturally fall asleep.
There is a certain point where the promised benefits of brainwave entrainment become more esoteric, and based on internal, subjective experience of oneself.  A few examples would be that listening to brainwave entrainment on a regular basis helps to increase one’s self-awareness, or that it increases mental “sharpness”, or helps to heal emotional trauma and increase your tolerance of stress and negative emotion. 
When making an educated decision on what product is best for you, it is important to have a general understanding of how the technology works, and what the benefits are of visiting the specific brainwave states.  Please click the link to visit a more detailed article –  How Does Brainwave Entrainment  Work, and the benefits of Alpha, Theta, Delta, and Gamma brainwaves.
In physics, entrainment is the process of two oscillating systems coming to assume the same periodic rhythm, such as is observed when two clocks slowly synchronize their ticking and tick together in harmony after some time. Pendulums also achieve this same synchronicity when swinging in close proximity to one another, a phenomenon first observed and written about in 1665 by Christiaan Huygens, a Dutch scientist.
I haven’t seen any research relating to using brainwave entrainment/isochronic tones and bodybuilding, so I’m afraid I don’t know how effective it would be to help with that. I have a few different tracks for increasing energy but I recommend this 1-hour track, which would fit better than my shorter tracks for a training session: The effects from these tracks are mainly felt while you listen to them, so I recommend listening to the energy tracks while you are training/lifting weights etc. I don’t currently have any tracks to help trigger the testosterone hormone.
Isochronic tones work just the same in delta as they do in alpha, theta and beta and they are widely used in the brainwave entrainment community to help people sleep. Like you, I’ve also seen some websites saying they don’t work in delta, but it’s a bit like the game of Chinese Whispers, where someone makes a comment and then after it gets passed around and shared a lot the message gets distorted and appears to be a fact. I don’t know of any scientific reason why they wouldn’t work in delta. I remember some people talking about this on a brainwave entrainment forum many years ago. They were saying they found isochronic tones a bit too abrupt for using to help them sleep and they preferred binaural beats, as they thought they were a more soothing sound. That was just a personal preference shared by a couple of prominent forum members at the time and some people then took that as a fact for everyone. That’s where I think that belief originated from.
Both brainwave entrainment and neurofeedback deal with brainwaves, but the similarity stops there. Entrainment pushes your whole brain into a pre-determined state, while neurofeedback teaches you how to move specific parts of your brain on your own. It is the differeence between forcing the brain into a given position, and skills building so you can move it there yourself.