7.1 Progressive Resistance Exercise and Muscle Strengthening

Progressive Resistance Exercise and Muscle Strengthening

Therapeutic exercise serves as the cornerstone of modern physical therapy rehabilitation. Restoring muscular force generation, endurance, dynamic stability, and power requires a rigorous application of exercise science principles. When prescribing therapeutic exercise, physical therapists must manipulate load, volume, velocity, and contraction type to drive targeted neuromuscular and tissue-level adaptations while safeguarding healing tissues.

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Foundational Principles of Exercise Conditioning

Resistance training is planned around the patient's goal, baseline capacity and restrictions. Use the response to one session and the recovery before the next session to guide progression.

Specificity, Overload and Reversibility

• Specificity (SAID): Adaptations reflect the task and dose, including muscles used, range, speed and contraction demands. For example, seated knee extension can build quadriceps capacity. Practice stair ascent as well if climbing stairs is the goal. Neural changes contribute to early gains and muscle adaptation develops with continued exposure. Measured early changes in muscle size can include swelling.
• Progressive overload: Increase challenge as capacity improves. Change load, repetitions, sets, range, leverage or task complexity according to the goal. Shorter rest or faster movement changes the training demand and can affect the load or technique a person can sustain.
• Reversibility: Gains can diminish after reduced training. The time course differs across people and outcomes. A reduced maintenance dose can preserve some gains. Check actual performance when adjusting the dose or resuming after an interruption.

Volume example: For the same exercise, three sets of eight at 20 kg give an external volume-load estimate of $3 \times 8 \times 20 = 480$ kg-repetitions. Track the load alongside range, technique and the number of good repetitions the patient could still perform. An equal volume-load estimate can be achieved with different combinations that produce different demands.

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Neuromechanical Types of Muscle Contraction

Describe muscle action by whether the active muscle–tendon unit is shortening, lengthening or holding approximately the same length. In movement analysis, consider the muscle's action as well as the direction and acceleration of the joint.

Active muscle–tendon action
├─ Isometric: develops tension at a near-fixed overall length
├─ Concentric: shortens while developing tension
└─ Eccentric: lengthens while developing tension

Isometric

An isometric task holds joint position approximately steady. The active and passive moments and external moments balance at that joint in a static example. Muscle fascicles can still shorten as the tendon stretches. Isometric strength gains tend to be greatest near the trained position, with variable transfer to other positions. Use a permitted angle and effort when motion is restricted or when a task requires holding a position. Sustained or intense contractions can limit local perfusion and raise blood pressure. The response varies with intensity, duration, muscle mass and breathing.

Concentric and Eccentric

In a controlled heel raise, the plantar flexors shorten while lifting the body and lengthen under load while lowering. Net torque determines angular acceleration. At constant joint velocity, the summed moments can balance in either direction. In a simplified force–velocity relationship, maximal force during shortening falls as shortening speed rises. Lengthening can sustain high force at a lower metabolic cost than shortening at a comparable mechanical workload. Actual force depends on task, speed, length and activation.

• Tendon loading: Controlled eccentric exercise places tensile load on the muscle–tendon unit. Load can also be progressed using exercise that includes both shortening and lengthening phases.
• Alfredson eccentric heel-drop programme: The original midportion Achilles study used three sets of 15 heel lowers in each of two positions, one with the knee straight and one with it bent. Participants repeated the sequence twice daily for 12 weeks. The affected side lowered the heel and the other side helped return to the starting position. This is one studied programme. Choose the current dose and range according to tendon location, irritability and response.

Isokinetic Testing and Training

A dynamometer limits movement to a selected angular speed once the participant reaches it in the isokinetic part of the arc. The device accommodates the torque the person applies. Output can vary with pain, effort, joint angle and testing setup. Standardize position, range, speed, repetitions and contraction mode before comparing peak torque or work. Specify which muscles form the numerator and denominator when reporting a strength ratio.

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Open vs. Closed Kinetic Chain Resistance Training

In an open-chain exercise the distal segment can move freely, as in a seated knee extension. A closed-chain task constrains distal motion through contact with a support, as in a squat or push-up. Both can train strength. Joint loading depends on the load location, joint angles and muscle forces.

• ACL rehabilitation: Load and knee angle affect graft demand during open-chain knee extension. After an isolated reconstruction, the Aspetar guideline allows limited-range work from around week 4, such as 90 to 45 degrees of knee flexion. Progress with symptom monitoring and the operative plan.
• Functional loading: A supported mini-squat trains coordinated loading across several joints. Use the permitted range and adjust for movement quality, pain and effusion.
• Patellofemoral loading: In one biomechanical comparison, stress was greater in the deeper squat angles and in the shallower knee-extension angles of the tested tasks. The resistance profile matters. Choose the specific range and dose using the patient's condition and response.

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Progressive Resistance Training Progression Models

A repetition maximum (RM) is the heaviest load the person can lift for the specified number of repetitions with the defined technique and range. A clinician can use submaximal performance to guide loads when RM testing is inappropriate.

Both groups in the comparison performed a separate general warm-up. The DeLorme work sets build toward the heaviest load, and the Oxford sets start at that load and reduce it as fatigue accumulates. For a 20 kg 10RM, the respective sequences are 10, 15 and 20 kg or 20, 15 and 10 kg. These are historical progression models and can be adapted to clinical capacity.

Daily Adjustable Progressive Resistance Exercise (DAPRE)

Knight described a performance-based model that uses an estimated 6RM. In the classic four-set structure, the first two sets prepare for a third set at the working load. The number of technically acceptable repetitions in the third set guides the fourth-set load. The fourth-set performance informs the next session's starting load.

Estimated working load → Preparatory sets → Working set at estimated 6RM
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                             Adjust fourth set to performance
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                         Use fourth-set result to guide next session

If a cleared patient completes nine controlled repetitions at an estimated 6RM load, performance supports a higher load for the next set within the protocol and the patient's restrictions. If technique degrades or symptoms rise, reassess before adding resistance. Published variants use different increments, and repetition-max testing or training to failure is optional in general exercise prescription.

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ACSM Evidence-Based Resistance Training Guidelines

The 2026 ACSM position stand addresses healthy adults. It identifies ways to emphasize different goals within progressive resistance training. Use a separate clinical protocol when healing, medical risk or symptoms constrain loading.

For a new or deconditioned patient, choose a manageable load and repeatable movement. A patient completing the planned repetitions with stable technique and symptoms and adequate recovery may be ready for a small progression. Adjust one meaningful variable so you can assess its effect.

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Clinical Safety Considerations: The Valsalva Maneuver

The Valsalva maneuver is forced expiration against a closed glottis or an imposed expiratory resistance. A standardized maneuver has a characteristic blood pressure response. Actual responses depend on effort, duration, position and autonomic function.

I   Start strain       → brief mechanical rise in arterial pressure
II  Continue strain    → early pressure fall, then baroreflex recovery
III Release strain     → brief mechanical fall in arterial pressure
IV  After release      → pressure overshoot and reflex slowing in a typical response

During early phase II, raised intrathoracic pressure reduces venous return and stroke volume. Sympathetic activation can raise heart rate and vascular resistance, helping pressure recover later in phase II. The pressure falls briefly when the strain ends in phase III. In phase IV, venous return and output recover while vascular resistance remains elevated. This can produce a transient overshoot and reflex slowing of the heart.

Heavy lifting can elicit high pressures during exertion from several mechanisms, including muscle compression, the pressor response and breath-holding. The timing and magnitude of those lifting measurements should be distinguished from the phases of a standardized Valsalva test. During supervised rehabilitation, choose a tolerable load and teach continuous breathing, such as exhaling through the effort. Use the patient's medical and surgical restrictions and stop and assess new chest symptoms, presyncope or an abnormal monitored response.

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Delayed Onset Muscle Soreness (DOMS)

Delayed-onset muscle soreness (DOMS) can follow unfamiliar or unusually demanding exercise, especially eccentric work. It emerges hours later, often peaks over the next one to three days and generally subsides over several days. Soreness intensity gives limited information about tissue damage. Track recovery, movement quality and function to guide the next dose. Gentle activity can be used as tolerated. Severe or worsening pain, substantial swelling, marked weakness or dark urine warrants clinical assessment.