Is a gear cycle good enough to get a nice sweaty exercise ?
Absolutely! It doesn’t matter how many gears it has. You can exercise on a 1 speed or a 15 speed or a 33 speed if you feel like it. The number of gears is totally irrelevant. Many modern internal geared bikes only have 3-7 gears and you can get around just fine on them. The goal of exercise is different for everyone, but it generally involves getting your heart rate elevated for 15-20 minutes or more. If you ride around the block for 5 minutes, you won’t get much from it. If you ride up hills and things like that for 15 minutes, you will get a little good from it. If you ride up hills and work really hard at it, monitoring your heart rate and tracking your progress, getting your heart rate up for 40 minutes to an hour, you will find your fitness level rapidly improving. If you are inclined to do more than that, you will get even better fitness improvements. The key for a bicycle is to make sure that all the important parts are well maintained and work properly. Do yourself a favor and
