Group classes at Gym Forty Five Amsterdam. At Gym Forty Five, we believe in the power of training together. Our group classes are intensive, personal, and always take place in small groups, so you get the attention you deserve. Whether you want to strengthen your core and lower body, improve your overall fitness, or prepare for a Hyrox competition: we have the right class for you. Our classes: BBB (Belly, Butt & Body) – Targeted training for your core and lower body. Tight, strong, and effective. Circuit Training – A versatile class where you alternate different exercises for a full-body workout. Hyrox Training – Specific preparation for the Hyrox competition. Combine running with functional fitness and go for your best time. Small groups. Great results.