7.1 Biomechanical Approaches: ROM, Strengthening & Endurance

Biomechanical Approaches: ROM, Strengthening & Endurance

The Biomechanical Frame of Reference is a foundational, bottom-up remediation approach in occupational therapy aimed at restoring structural stability, joint mobility, muscle strength, and physical endurance. It operates under the foundational premise that purposeful physical activity, graded exercise, and ergonomic adaptation can remediate musculoskeletal impairments, enhance physiological capacity, and directly improve functional performance in Activities of Daily Living (ADLs) and Instrumental ADLs (IADLs).

Certified Occupational Therapy Assistants (COTAs), under the supervision of Occupational Therapists (OTRs), implement biomechanical interventions across diverse clinical settings—including acute orthopedic trauma, post-surgical joint reconstructions, cumulative trauma disorders, spinal cord injuries, burns, and cardiopulmonary deconditioning.

1. Types of Muscle Contractions

Therapeutic exercise prescription requires a precise biomechanical understanding of skeletal muscle physiology and contraction dynamics. Skeletal muscle contractions are categorized based on changes in muscle fiber length, internal muscle tension, and joint angular displacement:

+-----------------------------------------------------------------------------+
|                   PHYSIOLOGICAL MUSCLE CONTRACTION TAXONOMY                 |
|                                                                             |
|   [1. ISOMETRIC (STATIC)]    ---> Internal tension developed; NO change in  |
|                                   muscle length or joint angle.             |
|                                   Ex: Holding grocery bag, pushing wall.    |
|                                                                             |
|   [2. ISOTONIC (DYNAMIC)]    ---> Internal tension developed; muscle length |
|                                   and joint angle change under constant load|
|      • Concentric            ---> Muscle SHORTENS as tension overcomes load |
|                                   (Acceleration / Positive work).           |
|      • Eccentric             ---> Muscle LENGTHENS while controlling load   |
|                                   (Deceleration / Braking / Negative work). |
|                                                                             |
|   [3. ISOKINETIC (VARIABLE)] ---> Constant angular velocity with dynamically|
|                                   accommodating resistance throughout ROM.  |
|                                   Requires specialized computerized machinery
+-----------------------------------------------------------------------------+

Comprehensive Muscle Contraction Matrix

[!IMPORTANT] The Force-Velocity Relationship & Eccentric Loading: In skeletal muscle physiology, eccentric contractions generate 20% to 40% more peak force than maximal isometric or concentric contractions while consuming significantly less oxygen and adenosine triphosphate (ATP). However, because eccentric loading places massive tensile stress on connective tissue and sarcolemma, it triggers significant micro-trauma, resulting in DOMS. COTAs must educate clients that mild muscle tenderness 1 to 2 days after eccentric training is normal, but sharp joint pain is pathological.

2. Progressive Resistive Exercise (PRE) Protocols

Progressive Resistive Exercise (PRE) is an evidence-based biomechanical training methodology designed to systematically increase skeletal muscle hypertrophy, neuromuscular recruitment, and tensile strength. PRE relies directly on the Overload Principle, which states that for a muscle to increase its strength, it must be challenged against a resistance greater than that to which it is accustomed.

10-Repetition Maximum (10-RM) Determination

The benchmark for PRE prescription is the 10-Repetition Maximum (10-RM)—the maximum amount of weight or resistance a client can lift dynamically through the complete, available range of motion for exactly 10 consecutive repetitions with correct form and without compensatory movements.

+-----------------------------------------------------------------------------+
|               PROGRESSIVE RESISTIVE EXERCISE (PRE) PROTOCOLS                |
|                                                                             |
|   [DELORME PROTOCOL] (Ascending / Progressive Loading)                      |
|   • Set 1: 10 repetitions @ 50% of 10-RM  ---> Warm-up / Motor preparation. |
|   • Set 2: 10 repetitions @ 75% of 10-RM  ---> Moderate overload.          |
|   • Set 3: 10 repetitions @ 100% of 10-RM ---> Maximal overload & fatigue.  |
|                                                                             |
|   [OXFORD TECHNIQUE] (Descending / Regressive Loading)                      |
|   • Set 1: 10 repetitions @ 100% of 10-RM ---> Maximal effort when fresh.   |
|   • Set 2: 10 repetitions @ 75% of 10-RM  ---> Accommodates emerging fatigue|
|   • Set 3: 10 repetitions @ 50% of 10-RM  ---> Maintains form under fatigue.|
+-----------------------------------------------------------------------------+

Comparison: DeLorme Protocol vs. Oxford Technique

Grading Parameters: Strength vs. Endurance vs. Power

• To Increase Muscle Strength (Hypertrophy/Recruitment): High resistance, low repetitions (e.g., 6–12 reps at 70%–85% of 1-RM, 3–4 sets).
• To Increase Muscle Endurance: Low resistance, high repetitions (e.g., 15–25 reps at 40%–60% of 1-RM, 2–3 sets with short rest intervals $<60$ seconds).
• To Increase Muscle Power: Moderate load moved at maximal explosive velocity (e.g., 3–6 reps at 30%–60% 1-RM with rapid contraction speed).

3. The Range of Motion (ROM) Continuum & Stretching Interventions

Range of motion interventions are prescribed along a clinical continuum based on the client's medical stability, surgical healing precautions, pain thresholds, and manual muscle test (MMT) grades.

+-----------------------------------------------------------------------------+
|                        THE RANGE OF MOTION CONTINUUM                        |
|                                                                             |
|   [PASSIVE ROM (PROM)]                                                      |
|   • Movement produced entirely by an external force (therapist, machine,    |
|     healthy limb). Zero active client muscle contraction.                   |
|   • Goal: Maintain capsule mobility, prevent adhesions, stimulate synovia.  |
|                                    |                                        |
|                                    v                                        |
|   [ACTIVE-ASSISTED ROM (AAROM)]                                             |
|   • Client initiates active muscle contraction; external assistance         |
|     completes the movement through the remaining available arc.             |
|   • Indication: Muscle strength grades 2-/5 to 3-/5.                        |
|                                    |                                        |
|                                    v                                        |
|   [ACTIVE ROM (AROM)]                                                       |
|   • Client moves joint independently through available arc against gravity  |
|     without external assistance or added resistance.                        |
|   • Goal: Maintain mobility, improve strength up to 3/5, enhance venous pump|
|                                    |                                        |
|                                    v                                        |
|   [ACTIVE RESISTIVE ROM (ARROM)]                                            |
|   • Movement against external mechanical or manual load (weights, bands).   |
|   • Goal: Build muscular strength (MMT > 3+/5) and physical endurance.     |
+-----------------------------------------------------------------------------+

Clinical Comparison of ROM Modalities

Stretching Principles: Low-Load Prolonged Stretch vs. High-Load Brief Stretch

When contractures or soft tissue shortening occur, the biomechanical gold standard is Low-Load Prolonged Stretch (LLPS):

• Mechanism: Applying a low, gentle force over an extended duration (15 to 30+ minutes via dynamic splinting, serial casting, or static progressive orthoses) allows the viscoelastic connective tissue to undergo plastic elongation (creep) without triggering protective muscle spasms or micro-tearing.
• High-Load Brief Stretch (HLBS): Forceful, rapid stretching triggers the myotatic stretch reflex (muscle spindle activation), causing protective muscle guarding, micro-vascular trauma, inflammation, and eventual rebound fibrosis/heterotopic ossification. HLBS is strictly contraindicated in contracture management.

4. Joint End-Feels: Normal vs. Pathological Classifications

An end-feel is the distinct subjective sensation perceived by the clinician when a joint is passively moved to the absolute limit of its available range of motion. Accurate identification of end-feels enables the COTA to determine the anatomical structure limiting motion and recognize acute pathology.

+-----------------------------------------------------------------------------+
|                        JOINT END-FEEL CLASSIFICATION                        |
|                                                                             |
|   [NORMAL / PHYSIOLOGICAL]                  [ABNORMAL / PATHOLOGICAL]       |
|   • SOFT: Soft tissue approximation.        • EMPTY: Movement stopped by    |
|     Ex: Elbow flexion (biceps/forearm).       severe pain, no physical stop.|
|   • FIRM: Capsular / ligamentous tension.   • SPASM: Sudden involuntary     |
|     Ex: Shoulder ER, ankle dorsiflexion.      muscle contraction / guarding.|
|   • HARD: Bone-on-bone contact.             • SPRINGY BLOCK: Intra-articular|
|     Ex: Normal elbow extension (olecranon).   rebound (meniscal tear).      |
|                                             • BOGGY: Spongy edema / effusion|
|                                             • ABNORMAL HARD: Premature bone |
|                                               stop (myositis ossificans).   |
+-----------------------------------------------------------------------------+

Detailed Joint End-Feel Matrix

5. Energy Conservation & Work Simplification: The 4 Ps

Energy conservation and work simplification techniques are systematic behavioral and biomechanical adaptations designed to reduce cardiopulmonary fatigue, metabolic demand, and joint strain during daily life. These strategies are paramount for clients with Chronic Obstructive Pulmonary Disease (COPD), Congestive Heart Failure (CHF), Multiple Sclerosis (MS), Parkinson's disease, and post-COVID fatigue syndrome.

The 4 Ps Framework

1. Pacing:
   • Spread energy expenditure evenly throughout the entire day rather than rushing.
   • Alternate between demanding physical activities (e.g., vacuuming, showering) and sedentary recovery tasks (e.g., reading mail, folding laundry while seated).
   • Take scheduled 5- to 10-minute rest breaks before exhaustion sets in.
   • Incorporate Pursed-Lip Breathing (inhale through nose for 2 counts, exhale through pursed lips for 4 counts) and Diaphragmatic Breathing during exertion to prevent air trapping and dyspnea.
2. Planning:
   • Create a weekly activity schedule, spacing strenuous chores across several days.
   • Gather all required supplies and tools before initiating a task (mise en place).
   • Store high-frequency items in the Golden Ergonomic Zone (between waist and chest height, 28–48 inches from floor) to eliminate bending, squatting, and overhead reaching.
   • Prepare double-batch meals and freeze half for low-energy days.
3. Prioritizing:
   • Identify essential tasks vs. non-essential activities.
   • Delegate heavy chores (e.g., carrying 40-lb water softener salt, scrubbing floors, lifting wet laundry) to family or community resources.
   • Utilize convenience items (e.g., pre-chopped groceries, robotic vacuums, online grocery delivery).
4. Positioning & Biomechanics:
   • "Never stand when you can sit; never lift when you can slide!"
   • Sit on a sturdy shower chair during bathing and a high task stool during meal preparation and ironing.
   • Adjust working countertops so forearms rest comfortably at $90^\circ$ elbow flexion with relaxed shoulders.
   • Slide heavy pots, laundry baskets, and grocery bags across counters or use a rolling utility cart rather than lifting and carrying.

6. Metabolic Equivalent of Task (MET) Levels & Cardiac Rehabilitation Phases

A Metabolic Equivalent of Task (MET) is an objective physiological unit used to quantify the energy expenditure and oxygen consumption of physical activities. 1 MET equals the basal metabolic rate of an adult at rest, defined as: $\text{1 MET} = 3.5\text{ mL of } O_2 \text{ consumed per kilogram of body weight per minute } (3.5\text{ mL } O_2/\text{kg}/\text{min})$

+-----------------------------------------------------------------------------+
|                     MET LEVEL STRATIFICATION ACROSS ADLS                    |
|                                                                             |
|   [MET 1.0 - 2.0] ---> Seated self-care: eating, seated sponge bath,        |
|                        brushing teeth, shaving, typing.                     |
|                                                                             |
|   [MET 2.0 - 3.0] ---> Seated warm shower, dressing/undressing, preparing   |
|                        cold breakfast, walking 2 mph.                       |
|                                                                             |
|   [MET 3.0 - 4.0] ---> Standing warm shower, making beds, sweeping floors,  |
|                        ironing, walking 3 mph.                              |
|                                                                             |
|   [MET 4.0 - 5.0] ---> Hot standing shower, vacuuming, light gardening,     |
|                        carrying 15–20 lb groceries, walking 3.5 mph.        |
|                                                                             |
|   [MET 5.0 - 6.0] ---> Scrubbing floors, shoveling light snow, cycling 10mph|
|                                                                             |
|   [MET 6.0+]      ---> Vigorous sports, digging ditches, carrying heavy loads|
|                        upstairs, running (>5 mph).                          |
+-----------------------------------------------------------------------------+

The Three Phases of Cardiac Rehabilitation

7. Clinical Scenario: Post-Surgical Cardiac & Orthopedic Intervention

Clinical Case Vignette: A 67-year-old client is admitted to the acute inpatient rehabilitation unit on Day 4 following a coronary artery bypass graft (CABG $\times 3$) and concomitant right rotator cuff debridement. The client is restricted to Phase 1 Cardiac Rehabilitation (MET ceiling $\le 3.0$) and strict sternal precautions (no lifting $>5\text{–}8\text{ lbs}$, no pushing/pulling with arms, no bilateral shoulder abduction/flexion $>90^\circ$). The orthopedic order allows right shoulder Active-Assisted ROM (AAROM) up to $90^\circ$ flexion.

COTA Treatment Plan & Session Execution:

1. Vital Signs & Baseline: Baseline vitals seated: HR 74 bpm, BP 122/78 mmHg, SpO2 97%. Borg RPE is 6.
2. Activity Selection: The COTA selects seated upper body grooming and dressing (2.0 METs) and gentle right shoulder table-top dowel slide exercises (AAROM within $90^\circ$ arc).
3. Ergonomic & Sternal Precaution Coaching:
   • The COTA trains the client to log-roll for bed mobility and push up from the bed using the lower extremities and a hugging-pillow technique across the chest (eliminating unilateral arm pushing).
   • The client is instructed in pursed-lip breathing during upper extremity movement.
4. Session Monitoring & Response: During seated grooming, the client's HR rises to 88 bpm (within safe $+14\text{ bpm}$ margin), BP is 130/82 mmHg, and RPE is 11. The client completes the session with zero angina or dyspnea, achieving target therapeutic goals safely.