Keiser Strength Series (A250, A300, A400)

Powered by Pneumatic Air Resistance

Unlike traditional weight-stack equipment, Keiser strength machines use pneumatic air resistance to deliver an exceptionally smooth, consistent workout. By using compressed air instead of heavy iron weights, resistance remains controlled throughout the entire movement and can be adjusted in precise, small increments.

This unique technology allows users of all fitness levels—from rehabilitation clients and older adults to elite athletes—to train with the exact resistance they need.

Why Air Resistance Matters

• Smooth, consistent resistance at any speed
• Precise resistance adjustments in small increments
• Low-impact training that’s easier on joints
• Ideal for power and speed training
• Suitable for rehabilitation, general fitness, and athletic performance

Train Through the Full Movement

Keiser machines provide resistance during both the lifting and lowering phases of an exercise.

• Concentric (lifting phase): Resistance is applied as muscles contract and shorten.
• Eccentric (lowering phase): Resistance continues as muscles lengthen under control.

This full-range resistance helps users build strength more effectively while maintaining proper control throughout every repetition.

Advanced Eccentric Training

Keiser’s technology also supports accentuated eccentric (“heavy negative”) training, allowing users to place greater emphasis on the lowering phase of an exercise. This advanced training method can help maximize strength development and athletic performance.

Not Hydraulic Technology

Although Keiser machines use cylinders, they are not hydraulic machines.

Hydraulic equipment simply resists movement and typically only works while the user is pushing or pulling. Keiser’s pneumatic system creates true resistance throughout the exercise, providing a more complete strength training experience with both lifting and lowering resistance.