2.5 Therapeutic Exercise Principles
Key Takeaways
- Overload, specificity, and progressive overload (the SAID principle — Specific Adaptation to Imposed Demands) drive every therapeutic exercise program.
- Strength dosing per American College of Sports Medicine (ACSM): 60-80% of one-repetition maximum (1RM) for 8-12 reps, or higher loads at ≤6 repetition maximum (RM) for advanced strength; hypertrophy targets 8-12 RM; muscular endurance uses ≤50% 1RM for 15+ reps.
- Closed kinetic chain (CKC) exercise (e.g., squat, leg press) co-contracts agonists and antagonists and is preferred early after lower-extremity surgery; open kinetic chain (OKC) (e.g., seated knee extension) isolates and is added later.
- Muscle contractions: isometric (no length change), concentric (shortening), and eccentric (lengthening); eccentric loading produces more force and more delayed-onset muscle soreness (DOMS) than concentric.
- Plyometric and high-impact training is reserved for late-stage rehab after the patient demonstrates adequate strength, neuromuscular control, and tissue healing per the plan of care (POC).
Foundational Principles
Overload, Specificity, Progression
- Overload: Tissues adapt only when loaded above their habitual demand.
- Specificity (SAID — Specific Adaptation to Imposed Demands): Adaptations are specific to the imposed stress — muscle, joint angle, contraction type, speed.
- Progression: Once a stimulus is tolerated, dosage is advanced to continue adaptation.
- Reversibility: Gains are lost when the stimulus stops.
- Individuality: Genetic, age, and pathology factors shape response.
FITT-VP Framework
Frequency, Intensity, Time, Type, Volume, and Progression — used by the PTA to document the exact dosage delivered within the plan of care (POC).
Dosing for Different Goals
The American College of Sports Medicine (ACSM) targets used on the NPTE-PTA:
| Goal | Intensity (% 1RM or RM) | Reps | Sets | Rest |
|---|---|---|---|---|
| Maximal strength | 80-100% 1RM (≤6 RM) | 1-6 | 2-6 | 2-5 min |
| Hypertrophy | 67-85% 1RM (8-12 RM) | 8-12 | 3-6 | 30-90 sec |
| Local muscular endurance | <50-67% 1RM (≥15 RM) | 15+ | 2-4 | <30 sec |
| Power (general) | 30-60% 1RM (upper); 0-60% 1RM (lower) | 3-6 fast reps | 3-6 | 2-5 min |
RM = repetition maximum, the heaviest load that can be lifted for the stated number of repetitions with good form.
Closed vs Open Kinetic Chain
- Closed kinetic chain (CKC): The distal segment is fixed (foot on the floor, hand on the wall). Examples: squat, leg press, push-up, lunge. CKC co-contracts agonist and antagonist groups and approximates joint surfaces — favored early after surgery to protect grafts (e.g., ACL).
- Open kinetic chain (OKC): The distal segment is free. Examples: seated knee extension, biceps curl, leg curl. OKC isolates muscle groups and creates more shear at the moving joint. Used selectively when isolation is the goal.
Muscle Contraction Types
| Contraction | Description | When to Use |
|---|---|---|
| Isometric | Tension without length change | Early rehab when motion is restricted (post-op week 1 quad sets) |
| Concentric | Muscle shortens; force generated < resistance overcome | Bulk of TherEx programs |
| Eccentric | Muscle lengthens under load; high force production | Tendinopathy (lateral epicondylalgia), late-stage strength, deceleration training |
| Isokinetic | Constant velocity using a dynamometer | Objective strength testing, athletic re-conditioning |
Eccentric training is well supported in tendinopathy management — the Alfredson protocol for Achilles tendinopathy and Tyler twist for lateral epicondylalgia are common PTA-implemented examples.
Plyometrics
Plyometric drills (box jumps, depth jumps, lateral hops) train the stretch-shortening cycle. They are placed late in a rehab progression once the patient demonstrates:
- Pain-free full ROM
- Adequate strength (often ≥80% limb symmetry index for LE programs)
- Adequate single-leg balance and squat control
- Surgeon clearance for impact
Volume and Recovery
- DOMS typically peaks 24-72 hours after unaccustomed eccentric loading.
- 48-72 hours between heavy resistance sessions for the same muscle group is a standard rest guideline.
- The PTA monitors pain, swelling, and effusion sign — increased symptoms persisting beyond 24 hours after a session suggest the prior dose was excessive and dosage should be reduced within the POC.
A PTA is implementing a strengthening program 14 weeks after ACL reconstruction. The plan of care directs hypertrophy-level dosing for the quadriceps. Which set/rep/load scheme BEST matches that goal?
A patient with lateral epicondylalgia has plateaued on isometric and concentric wrist extensor exercises. Which exercise modification has the strongest evidence to add next within a PTA-implemented program?