Strength training is work which challenges your muscles with resistance. The basic formula is to use 4 to 6 repetitions to increase strength, 8 to 10 repetitions for general increases in muscularity and fitness and anything more than that begins to build muscle endurance. The effect on muscle from spinning is building endurance.
There is no such thing as muscle tone, that is a marketing term which misuses the term tonus. Tonus is the resistance of a muscle to pressure and is not visible. The removal of fat overlying muscles makes them appear more prominent which marketers term tone.
Strength training is the second most important factor in fat loss, nutrition is first and cardio is third. The benefits of strength training are far more numerous than those of cardio. Doing full body and compound movement strength exercises will not only aid in fat loss it will also improve your ability to do cardio. World class cyclists cross train with strength training to supplement and improve their ability to cycle.
Your legs are sore because the body improves cardio more rapidly than it does the musculoskeletal system. Your heart rate is an indicator of how hard your cardio system is working and is not the only measure of the work you are doing.
It is called WORK-ing out for a reason.
I said getting fit was simple, I did not say it was easy.
Cardio burns calories, strength work burns fat.
Eat well to lose weight, exercise to get fit
You can not build a six pack using twelve packs
Often when we seek a magic bullet for fitness we end up shooting ourselves in the foot.
"I think calories are little germs in food that all moms are afraid of" Dennis the Menace