The most common image for a gym or fitness center to feature on their logo is one of the human body. The form can be either masculine and muscular or a slim, feminine shape depending on the message that you want to convey.
Exercise equipment such as barbells, dumbbells and treadmills can work well. A symbol such as a heart could emphasize the health benefits of regular workouts.
Movement is a common theme in fitness logos and the images of people and other objects used on many designs are made to look like they are in a state of movement.
When it comes to choice of color, anything can work well. Color combination's that are vibrant and bright are common in this industry although conservative colors can also suit some types of gym or fitness club better.
Bear in mind that logos are usually more effective when they are simple in design. Using excessive color can make a logo unnecessarily cluttered so the best designers will usually stick to only two or three colors. This can also make for a more versatile image, especially when it comes to printing.
One more thing worth noticing with fitness and gym logos is that they often use fonts that slope forwards, implying movement, progress or speed.
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