Rabbits Beat Snails
Some exercisers set their cardio machines to slow every workout under the misconception that moving at a snail's pace burns more fat. The truth is that varying pace and intensity and mixing fast and slow speeds is a far more successful weight loss strategy since it addresses the body's different energy systems and muscle groups.
Locking your feet under something to do sit ups may seem like a good idea but it is more likely to injure your lower back than flatten your abdomen. Anchoring your feet means most of the work is being done by the hips. To shift the work to the abs, lie on your back with your feet flat on the floor, extend your arms, and slowly roll up to a sitting position one vertebrae at a time; keep breathing as you move.
The Thighs Have It
You should skip the inner and outer thigh machines because they work such a small area of muscle and because the movements are so unnatural. You may end up building the very area you are trying to trim. For toned legs, better results are obtained using exercises such as holding a weighted ball as you do basic squats, lunges, and side squats.