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Safe Training: Getting Started, Injury, and Age

Much of what is commonly repeated about workout safety does not hold up against the data: stretching beforehand does not prevent injury, machines are not safer simply because they are machines, and age does not eliminate the response to resistance training. What actually prevents injury is resistance training with progression. Here are the rules the Letz safety filter uses to select exercises whenever someone logs pain or a condition.

Rules and studies

  1. 01Warm-up and stretchingWarming up improves performance in most cases; prolonged static stretching before training can reduce strength and power, whereas dynamic stretching does not impair performance.The guided session starts with warm-up sets of the specific exercise; static stretching is saved for the end of the workout or mobility days.
  2. 02Resistance training for injury preventionStrengthening programs substantially reduced sports injuries; stretching alone showed no such effect.Users who log running or sports receive complementary strength work tailored to the sport's specific demands (swimming: rotator cuff and scapula; soccer: hamstrings and groin; dance: ankles and core), only when it does not compromise the workout routine.
  3. 03Free weights, machines, and bodyweightFree weights and machines produce similar strength and hypertrophy gains when directly compared; strength gains are specific to the trained modality.The plan is generated based on the equipment the person actually has and prefers; swapping one exercise for another within the same movement pattern does not reduce the quality of the plan.
  4. 04Resistance training in older adultsAdults aged 50 and older, including the oldest-old, gain strength and muscle mass with progressive resistance training.Age does not remove exercises from the plan; it reduces the suggested load increase and raises the target RIR.
  5. 05Menstrual Cycle and PerformancePerformance may be slightly lower during the early follicular phase, but the effect is trivial and highly variable; the recommended approach is individualized, not a rigid phase-based rule.Letz does not alter training plans based on cycle phase; coaches address reported symptoms and adjust the day using the same readiness logic applied to sleep and soreness.