8.6 Strengthening: Progressive Resistance Exercise & Loading Prescription
Key Takeaways
- Strengthening is one of two named sub-topics in the 11% Muscle Rehabilitation content area, the joint-largest weighting on the NBCE Physiotherapy Test Plan.
- The DeLorme progressive resistance protocol uses three sets of ten at 50%, 75%, and 100% of the ten-repetition maximum, while the Oxford technique reverses that order.
- Loads at or above roughly 85% of one-repetition maximum for two to six repetitions bias maximal strength; 67 to 85% for six to twelve repetitions biases hypertrophy.
- The SAID principle means adaptation is specific to the imposed demand, including contraction type, velocity, range of motion, and joint angle.
- Isometric strength gains are largely confined to about 20 degrees on either side of the trained joint angle, which limits their value as a sole strengthening method.
8.6 Strengthening: Progressive Resistance Exercise & Loading Prescription
Core Clinical Mandate: Muscle Rehabilitation (11%) names exactly two sub-topics — stretching and strengthening. Together with Neuromuscular Rehabilitation it ties for the second-largest weighting on the test plan. Strengthening questions are parameter questions: which contraction type, which chain, which load, how many repetitions, and how the load progresses.
Contraction Types and Their Force Characteristics
| Contraction | Muscle Length | Relative Force Capacity | Metabolic Cost | Typical Rehabilitation Role |
|---|---|---|---|---|
| Isometric | Unchanged | Moderate | Low | Earliest safe loading; painful or immobilized joints; arthrogenic inhibition |
| Concentric | Shortens | Lowest of the three | Highest per unit force | General strengthening; force production |
| Eccentric | Lengthens under load | Highest — roughly 20 to 40% greater peak force than concentric | Lowest per unit force | Tendinopathy; deceleration control; late-stage loading |
| Isokinetic | Varies at fixed angular velocity | Accommodates to effort through range | Moderate | Testing and controlled training where equipment exists |
Eccentric loading is the highest-force, lowest-cost option, which makes it uniquely effective for chronic tendinopathy and deceleration training — and also the most reliable producer of delayed onset muscle soreness, peaking 24 to 72 hours after an unaccustomed bout.
Isometrics: Useful but Angle-Specific
Isometric training produces strength gains that are largely confined to approximately 20 degrees on either side of the trained joint angle. Because of this "physiological overflow" limit, isometrics cannot serve as a complete strengthening program; a patient trained only at 60 degrees of knee flexion will not have gained meaningful strength at 10 degrees. They are, however, the right first choice when motion is contraindicated, when a joint is acutely painful, or when effusion is producing arthrogenic inhibition. Sustained isometric holds of roughly 30 to 45 seconds at moderate intensity also produce a useful analgesic effect in tendinopathy.
Blood Pressure Caution: Sustained maximal isometric contraction combined with breath-holding produces the Valsalva manoeuvre, sharply raising intrathoracic pressure and causing a marked rise in blood pressure followed by reduced venous return. Patients with hypertension, known cardiovascular disease, recent eye surgery, or abdominal wall weakness must be cued to exhale on exertion and avoid sustained maximal holds.
Open vs. Closed Kinetic Chain
| Open Kinetic Chain (OKC) | Closed Kinetic Chain (CKC) | |
|---|---|---|
| Distal segment | Free to move | Fixed against a surface |
| Example | Seated knee extension, biceps curl | Squat, lunge, push-up, leg press |
| Muscle action | More isolated, single-joint | Multi-joint co-contraction of agonists and antagonists |
| Joint forces | More shear, especially at end range | More compression, which is generally better tolerated |
| Proprioceptive input | Lower | Higher; more functional |
Clinical selection rules:
- After ACL reconstruction, open-chain knee extension in the terminal 0 to 30 degrees produces the greatest anterior tibial shear and is the range traditionally restricted in early rehabilitation. Closed-chain squatting to about 60 to 70 degrees is generally better tolerated early.
- In patellofemoral pain, patellofemoral joint contact pressure rises with increasing knee flexion in closed chain and with increasing extension in open chain. Working in a mid-range arc that avoids the painful zone in whichever chain is used is the practical solution.
- Closed-chain exercise is not automatically superior. It is more functional, but open-chain work is the better tool when a specific muscle is inhibited and stronger synergists will otherwise substitute for it.
Classical Progressive Resistance Protocols
DeLorme (1945) — The Original PRE
Based on the patient's 10-repetition maximum (10 RM), the greatest load that can be lifted exactly ten times with good form:
| Set | Load | Repetitions |
|---|---|---|
| 1 | 50% of 10 RM | 10 |
| 2 | 75% of 10 RM | 10 |
| 3 | 100% of 10 RM | 10 |
The first two sets act as a progressive warm-up. The 10 RM is retested periodically — classically weekly — and the loads recalculated.
Oxford Technique (Zinovieff)
The same three sets in reverse order: 100%, then 75%, then 50% of the 10 RM. The rationale is to load the muscle maximally while it is fresh and to reduce load as fatigue accumulates. The choice between DeLorme and Oxford is largely a matter of whether warm-up or fatigue accommodation matters more for the individual patient.
DAPRE (Daily Adjustable Progressive Resistive Exercise)
Knight's DAPRE removes the weekly retest by adjusting load within and between sessions based on performance:
| Set | Load | Repetitions |
|---|---|---|
| 1 | 50% of working weight | 10 |
| 2 | 75% of working weight | 6 |
| 3 | 100% of working weight | As many as possible |
| 4 | Adjusted based on set 3 | As many as possible |
The number of repetitions achieved in set 3 determines the adjustment for set 4, and the repetitions in set 4 determine the working weight for the next session. Its advantage is that it self-corrects daily for the fluctuating strength typical of early rehabilitation.
Repetition-Maximum Loading Zones
| Training Goal | Load (% 1 RM) | Repetitions | Sets | Rest Between Sets |
|---|---|---|---|---|
| Maximal strength | ≥85% | ≤6 | 2–6 | 2–5 minutes |
| Hypertrophy | 67–85% | 6–12 | 3–6 | 30–90 seconds |
| Muscular endurance | ≤67% | ≥12 | 2–3 | ≤30 seconds |
| Power (single-effort) | 80–90% | 1–2 | 3–5 | 2–5 minutes |
| Power (multiple-effort) | 75–85% | 3–5 | 3–5 | 2–5 minutes |
Reading the table correctly is the exam skill. Long rest periods go with heavy loads because the phosphagen system needs time to resynthesize ATP and creatine phosphate; short rest periods go with hypertrophy work because the accumulated metabolic stress is part of the stimulus. A question that pairs 85% of 1 RM with 30-second rests is describing an incoherent prescription.
Frequency and Volume
- Two to three non-consecutive sessions per week per muscle group is the standard rehabilitation starting point, allowing 48 hours for recovery and protein synthesis.
- Progressive overload requires that at least one variable increase over time: load, repetitions, sets, range, velocity, or stability demand — and preferably only one at a time, so cause and effect stay legible.
- The 2-for-2 rule is a simple, defensible progression trigger: when the patient can complete two extra repetitions beyond the target on the final set in two consecutive sessions, increase the load.
The SAID Principle and Specificity
Specific Adaptation to Imposed Demands. Adaptation is specific to:
- Muscle group and joint angle trained.
- Contraction type — eccentric training produces greater eccentric than concentric gain.
- Velocity — training slowly produces gains that are greatest at slow velocities.
- Range of motion — training through a partial range produces gains concentrated in that range.
- Energy system — heavy low-repetition work trains the phosphagen system; sustained work trains oxidative capacity.
- Posture and context — strength developed seated does not fully transfer to standing under load.
The practical corollary: the closer the exercise resembles the demand the patient must return to, the greater the transfer. A roofer who must carry bundles up a ladder needs loaded carries and step-ups, not seated leg extensions.
Sequencing a Strengthening Program
- Resolve the gate first. Effusion, acute pain, and arthrogenic inhibition block voluntary activation. Address them, or the strengthening simply will not take.
- Begin with isometrics at a non-painful angle, adding sub-maximal holds and, where voluntary activation is poor, NMES as an adjunct.
- Progress to concentric work through a pain-free range, typically light-load and higher-repetition at first to rebuild tolerance and technique.
- Add eccentric loading once tissue tolerance permits — the key transition for tendinopathy and for deceleration control.
- Move from open to closed chain and from single-joint to multi-joint as stability improves.
- Add velocity, then reactive and plyometric demand, last of all, and only once eccentric control is demonstrably sound.
- Re-measure. A strengthening program without repeated objective measurement — dynamometry, repetition maximum, single-leg hop symmetry, timed sit-to-stand — is not a program, it is an activity.
Sequencing Rule: Eccentric before plyometric, always. Plyometric training is a rapid stretch-shortening cycle that depends on the ability to absorb force eccentrically. Prescribing jumping to a patient who cannot control a slow single-leg lowering is how re-injury happens.
Special Populations
- Older adults: resistance training is safe and highly effective; power (velocity) training has particular functional value for stair negotiation and fall avoidance. Begin conservatively and progress on demonstrated tolerance.
- Osteoporosis: loading is beneficial for bone, but end-range spinal flexion under load is contraindicated because of vertebral compression fracture risk. Choose extension-biased and axially loaded patterns.
- Hypertension and cardiovascular disease: avoid sustained maximal isometrics and Valsalva; use moderate loads, higher repetitions, controlled breathing, and rhythmic patterns.
- Post-surgical patients: the surgeon's tissue-protection protocol overrides any general loading table.
A patient's ten-repetition maximum for a knee extension is 40 pounds. Using the classical DeLorme progressive resistance exercise protocol, what loads and repetitions should be prescribed?
A clinician prescribes three sets of four repetitions at 88 percent of one-repetition maximum but schedules only 30 seconds of rest between sets. Why is this prescription internally inconsistent?
A patient with a painful, effused knee cannot perform a knee extension through range. The clinician prescribes isometric quadriceps contractions at 60 degrees of flexion. What limitation should be explained to the patient?
Six weeks after anterior cruciate ligament reconstruction, which loading choice most respects graft protection while still strengthening the quadriceps?