If the comfrey is still liquid, it is okay. If the bottle is a little low, add some everclear to replace the evaporation. I am told in the reference books that comfrey tincture will last for a decade, with no loss of strength. Mine is used too quickly for that. The darker brown the tincture the better, because it is stronger, but even pale tincture will work well. It will turn your skin brown, but it washes off.

TENS...there is a LOT of information there! But lets start at the beginning. The acclimation takes 5 minutes or so (depending on the type of stimulation); BEFORE you turn up the second time. The stimulation uses up some of the neurotransmitter compound your body uses to send a pain signal. This compound is what carries the pain signal from nerve cell to nerve cell, to jump the gap from axiom to dendrite. Think of it as pain juice, When repeated signals are transferred, this juice gets used up locally, and the pain signals will no longer be carried. So what hurt as too high at first, is not as uncomfortable when this neurotransmitter (pain juice) is depleted. Then you can turn it up as high as you can take (higher is directly equal to pain relief) and let it run.

The scan frequencies are used to release endogenuos opiates (endorphines .and enkephalin) which are what the body uses to run away from danger, even when hurt. They work like Opiates (like Morphine), except without the needle. Every person releases these compounds at a different frequency, so the frequency scan covers everyone best.

Higher frequency pulses are more comfortable (80 to 120 Hz), But lower frequency pulses (1 to 15 Hz) release longer lasting relief. That said, a fixed frequency pulse will release some too, it just needs to run longer. The only limit to TENS is tolerance, too much and the muscles get sore.

However, the comfrey tincture should heal that soreness in a short while.

Let me know any time I can help you! :)