What is the best exercise/ fitness gym routine for a nocturnal person like me without developing muscles?

I am working in a call center. I am in a night shift. I also drink slimming coffee and diet pills but none seems to be working. . I am planning to enroll in a fitness gym but I think I can only have sessions during my day-offs usually Saturday and Sunday. I also just would like to lose weight and not develop hard muscles. Thanks.

The Heart of Yoga: Developing a Personal Practice

• ISBN13: 9780892817641
• Condition: NEW
• Notes: Brand New from Publisher. No Remainder Mark.

Product Description
The first yoga text to outline a step-by-step sequence for developing a complete practice according to viniyoga–yoga adapted to the needs of the individual. A contemporary classic by a world-renowned teacher. This new edition adds thirty-two poems by Krishnamacharya that capture the essence of his teachings. Sri Tirumalai Krishnamacharya, who lived to be over 100 years old, was one of the greatest yogis of the modern era. Elements of Krishnamacharya’s te. . . More >>

The Heart of Yoga: Developing a Personal Practice