A backpack is an excellent choice for the gym, often surpassing traditional duffel bags in terms of ergonomics and versatility. The primary advantage of a gym backpack is the dual-shoulder strap design, which distributes the weight of your gear—shoes, water bottle, lifting belt, and change of clothes—evenly across your back and shoulders. This is much better for your posture than a duffel bag, which puts all the strain on one side of the body. Many modern "athletic" backpacks are specifically designed with dedicated compartments, such as a vented shoe pocket at the bottom to keep your sweaty sneakers separate from your clean clothes, and water-resistant linings for wet towels or swimwear. They are also much more convenient if you commute to the gym via bicycle, public transit, or walking, as they keep your hands free. While a duffel bag might offer more raw "volume" for bulky items like yoga mats or boxing gloves, a well-organized 25-30 liter backpack is typically the "sweet spot" for most gym-goers, providing enough space for the essentials while remaining compact enough to fit into a standard gym locker without having to cram it in.