Exercise and Activity in Pain Management

Original Editor - Vinit Kothekar

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Introduction

The International Association for Study of Pain (IASP) defines pain as: "An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." It further states that: "Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life." IASP also argues that "[a]ctivity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain".

For people experiencing pain, their initial response is often to avoid activity and seek rest. However, exercise therapy is often considered an important treatment for pain management. There are many other additional benefits of exercise and regular physical activity, including:

• Controls weight
• Reduces risk of cardiovascular disease and metabolic disease
• Reduces risk of some cancers
• Strengthens bones and muscles
• Improves mental health and mood
• Improves ability to perform daily activities and prevent falls
• Increases chances of living longer

Exercise and physical activity not only have benefits for healthy individuals - they also have proven benefits in various patient populations. Because of this, some authors have explored the idea that exercise acts as a drug.

Exercise Induced Hypoalgesia (EIH)

EIH is phenomenon which has been extensively studied in the literature, but the mechanisms behind EIH are not fully understood. EIH is characterised "by elevations in pain threshold and tolerance as well as reductions in pain intensity ratings during and following exercise."

"The most commonly tested hypothesis for EIH is that exercise induces a release of endogenous opioids at either peripheral, spinal, and/or central sites: all of which contribute to pain modulation." Koltyn et al. note the following about the endogenous opioid mechanism:

• Muscle contractions activate A-delta and C fibres in skeletal muscle, the stimulation of which can lead to the activation of the endogenous opioid system
• Exercise can increase blood beta-endorphin contractions in males
• Peripheral afferent neuron stimulation might modulate pain by activating spinal / supraspinal inhibitory mechanisms

It is important to note, however, that early research in EIH and the opioid mechanism focused on pain-free adults/animals and the research on humans is "equivocal". There are also instances where "EIH that is insensitive to opioid antagonists" occurs.

• Another proposed mechanism for EIH is the endocannabinoid system. It is argued that exercise increases serum concentrations of endocannabinoids which may contribute to control of pain transmission. There may also be an association between the endocannabinoid and opioid systems where the activation of one system is mediated by the other.
• Animal experiments suggest that there may be an interaction between opioid and serotonergic mechanisms to cause EIH

Other theories behind EIH are discussed in detail in Exercise-induced hypoalgesia in pain-free and chronic pain populations: state of the art and future directions.

Effects of Different Types of Exercise in Pain Management

Pain control is achieved differently with different types of exercises. Prescribing appropriate intensity and frequency of exercise is important in achieving the desired effects of hypoalgesia.

Aerobic Exercise/Endurance Training

The effects of aerobic exercises on pain have been extensively studied in the literature. The intensity of the exercise should be well tolerated for the exercise to be effective. It has been said that the aerobic exercise should target larger muscle groups, involve repetitive muscle contraction and elevate the resting heart rate to the target heart rate for at least 20 minutes. The therapeutic window for aerobic training is extremely important, as some patients may exhibit worsening of symptoms secondary to exercise. Musculoskeletal pain is one of the side effects of exercise, thus achieving the right balance is very important. Too little exercise is not beneficial, but too much exercise can aggravate symptoms.

Various prescribed workloads have been suggested which result in EIH:

• Hoffman et al. found that 30 minutes of treadmill exercise at 75% of VO₂max resulted in a significant decrease in pain ratings. However, they found that there were no significant changes with 10 minutes of treadmill exercise at 75% VO₂max or 30 minutes at 50% VO₂max.

• A review by Koltyn found that hypoalgesia consistently occurs after high-intensity exercise, particularly with worloads of 200 W and higher. It also occurs with exercise at prescribed at 65 to 75% of VO₂max. Koltyn notes that results were not conclusive when percentage of a heart rate maximum was used a prescribing criteria or when subjects were allowed to select their own intensity.
  

Resistance Exercise/Strength Training

Very few studies have examined the relation of resistance training and pain modulation. However, a study done by Koltyn and Arbogastconcluded a single bout of resistance exercise can achieve a hypoalgesic response from resistance training. The resistance exercise consisted of 45 min of lifting 3 sets of 10 reps at 75% of 1RM, which included bench press, leg press, pull downs, and arm extensions.

Even though EIH has suggested to have a central response, EIH response was larger in exercising body part compared to non-exercising body part. A study done by Vaegter et al had their subjects perform 2 isometric contractions of dominant biceps brachii and quadriceps at 30% and 60% MVC. They concluded that high intensity isometric contraction by biceps brachii and quadriceps produced a larger local EIH compared to low intensity contraction.

Condition Specific

Therapeutic exercises are the primary choice of non-pharmacological treatment for chronic neck pain, chronic low back pain, complex regional pain syndrome, fibromyalgia, osteoarthritis and similar other unremitting pain syndromes.

An immediate local mechanical hypoaglesic response has been shown to specific exercises of cervical spine in patients having neck pain for at least 3 months. Specific exercises included (1) cranio-cervical flexion with 10 second contraction for 10 repetitions with 10 second hold in between, and (2) cervical flexion endurance exercise of head lift in supine was performed for 3 sets of 10 reps at 12RM with 30 second rest in between sets (each rep lasted for 3 second with 2 second interval between reps).

A systemic review done by Hayden et al, concluded that supervised exercise therapy which consists of stretching and strengthening, and is individually designed improves pain and function in chronic nonspecific back pain.

Martin et al designed an exercise program which has shown to be an effective management for fibromyalgia in short term. Exercise program included aerobic training, flexibility exercises and strength training.

Adverse Effects of Exercise

If exercise is considered a drug, adverse effects like any other drug follows. Exercise if not prescribed appropriately and in some cases even if prescribed appropriately may result in certain adverse effects.

It is typically accepted that exercise result in myofiber damage, and substances like lactate are release which provide nociceptive input in response to exercise. So there is a risk of flare up of symptoms after exercise. Exercise is considered a physical stressor and it has been known to activate stress responses in neuroendocrine system. And hence clinicians should be careful in prescribing exercises to patients in pain. As physical stress in small amount with adequate rest-recovery period may be optimal, but excessive stress may increase pain sensitivity.

Physical Activity

Bed rest and immobility more than 2 days have never been shown beneficial, and on the contrary in geriatric population it appears to be detrimental. Physical activities like Tai chi and Yoga has shown significant improvement in prevention and control of pain since ages. Ancient practice of Tai chi seems to be an effective intervention in osteoarthritis, low back pain and fibromyalgia. Yoga which traces its roots 500-200 BCE is an effective adjunctive treatment for chronic low back pain as proven by Holtzman et al in a meta-analysis. Regular physical activity help in preventing ill effects of immobility. It prevents joint stiffness, muscle tightness and helps in blood circulation. Other known physical activities like swimming and walking have shown to be effective in decreasing pain and improving function. A study by Ickmans K et al. provides evidence that rehabilitation programs have long-term effects on people with chronic pain. 

Conclusion

When prescribing exercise for pain management it is important that we:

1. Understand the parameters (i.e., mode, frequency, duration, intensity) of therapeutic exercise for pain relief.
2. Describe how to modify exercise parameters as they relate to the pain condition, age, psychosocial factors, and patient's health status.
3. Recognize the importance of implementing adjunct therapies to address issues related to exercise prescription (i.e., biopsychosocial, fear avoidance behaviour, catastrophizing, cognitive behavioural therapy).
4. Understand the importance of patient education in prescribing therapeutic exercise, including the concept of motivation, pacing) to enhance overall treatment effectiveness and compliance.