Gist
Yes. HIIT can improve athletic performance by raising aerobic capacity and repeated-effort conditioning, but the interval format should match the sport and complement strength, speed and skill work.
Yes. Bodyweight training can support athletic performance through relative strength, coordination, plyometric power and equipment-free conditioning, but advanced athletes may need additional external load.
Yes. Circuit training can support athletic performance by improving strength-endurance, general conditioning and work capacity, but it should complement sport-specific speed, power and skill training.
Yes, potentially. Kettlebell swings can improve hip power, maximal and explosive strength and conditioning, but direct transfer to sprinting and sport performance is mixed.
Yes. Calisthenics can support athletic performance through relative strength, body control, coordination and muscular endurance, but it should complement sport-specific speed, power and skill work.