Sennheiser MX75 Twist-To-Fit In-Ear Stereo Sport Headphones

Once I realized there was an R and L to these, they fit perfectly and worked great for my half-marathon a few weeks ago. I never adjusted them once and they did not hurt my ears. Sound is decent.

First off, some clarification.
If you look at the pics associated with this item... the man is not inserting the headphones in the ear correctly. He is twisting them posteriorly (backwards) so that they wedge into the ear to stay secure. They are designed to twist anteriorly (forward) so that the little "wheel" at the top of the earbud fits under the little flap that your ear makes as it attaches to your head.
If you insert them correctly... this makes them almost impossible to shake loose. In addition, the headphones come with multiple sizes of "wheels" to customize your fit. Also, there are multiple earbud speaker attachments to fit your ear-hole (as well as a set of cushioned covers).

These headphones are great for many applications. I use them while running and lifting. I even use them at sporting events, since they make a good seal and keep a lot of the crowd noise out and allow me to hear the radio broadcast.
The coiled wire can be a bit of a bother, but really is not a "deal breaker".
Overall, I would buy these again... actually I am buying some for family members this Christmas.

The earphone buds are too large and consequently cause pain after about 15 minutes, even when using the smaller fitting ring. The twist-to-fit is okayish, though it causes pain after a while, as the length of the twist-to-fit portion is fixed and may not match with your ear.

NOT recommended unless you have really large ears. May sound stupid, but that's the way it is.

Sound quality is good. But you dont care about sound quality if your ears hurt.

Sennheiser MX75 Twist-To-Fit In-Ear Stereo Sport Headphones
I bought the Sennheiser MX75 twist-to-fit headphones and have been mostly pleased with the purchase.

PRO: The twist-to-fit design fits my ear perfectly and allows me to hear better sound at a lower volume because it stays in place. I walk at a brisk pace and it stays in place without falling out, unlike other headphones I have owned. I have worn the earphones for as long as 1 1/2 hours at one time and they continued to be comfortable. However, my ears were not sweaty, which may make it less comfortable after a while as some reviews noted.

CON: I gave it 4 stars rather than 5 because, like many others who left reviews, I hate the curling wires. I prefer straight wires because they do not get twisted around everything they touch. However, I have learned how to store it in a way that lessens this issue. I also find that the wires, at times, have minds of their own and do not always stay where I want it to stay (they sometimes creep up to near my chin, which is annoying). Also, by design, the right wire is longer than the left wire. I personally like the wires to be the same length. The headphones are also not the nicest color (green), which makes it more conspicuous. I cannot comment on how well the wires hold up as I have only had these headphones for 2 weeks. So far, they seem to be made well.

Summary: I think the positives outweigh the negatives. I am still happy with the purchase because of the good sound quality and excellent fit for my ears. It is a good headphone choice if you exercise or use it while doing any sports activity, like brisk walking.

I've tried all kinds of earbuds, and these Sennheisers are definitely the best I've found in terms of staying put, even with fairly vigorous activity. Sound is good, too. Unfortunately the design, which helps lock the buds in place, also put a little pressure on the ear, meaning these are not the most comfortable I've ever used, But if you're tired of constantly repositioning earbuds, these may work well for you.