Physical Activity as Cause and Cure of Muscular Pain

Physical Activity as Cause and Cure of Muscular Pain: Evidence of Underlying Mechanisms – free full-text /PMC5473374/ – July 2017

This article interested me because I’ve long noticed that exercise both increases and decreases pain, usually initially increasing but over time (days or weeks) decreasing.

I’m always having to balance my activity and rest to keep a positive effect, doing both, but not too much of either one.

I had not paid attention to the difference between occupational (or physical) therapy (OT) and “leisure time physical activity” (LTPA). This article explains why I haven’t progressed much in my physical therapy routines: they involve static load, repetitive movements, and high peak forces, All of these are damaging to a body with a connective tissue disorder, like EDS. 

Key Points

• Physical activity (PA) includes the domains of leisure, occupation, and sleep, each having different profiles of intensity, duration, and repetitiveness of muscular activity and, therefore, different effects onmusculoskeletal health.
• Occupational PA often involves static load, repetitive movements, and high peak forces, all of which — if occurring for prolonged duration — are risk factors documented to compromise musculoskeletal health and to causally relate to muscle pain development.
• Physical exercise training can be planned to obtain health-enhancing effects and can be targeted toward maintaining and improving muscular strength, endurance, and resilience.
  Recent studies also show effects in pain reduction.
• An individual’s daily PA profile is the accumulated impact from all the domains of PA and should be balanced to counteract lifestyle diseases, including musculoskeletal disorders.
• The workplace offers an arena for exercise training that is beneficial for health. Future research must focus on how organizational, motivational, and financial aspects can be addressed across a range of workplaces to promote implementation and improve adherence to attain significant effects.

Editor’s note: Go online to view the Video Abstract in the Supplemental Digital Content: see http://links.lww.com/ESSR/A35.

INTRODUCTION

This article deals with the contrasting effects of physical activity (PA), which can cause muscular pain but also can reduce muscular pain, maintain function, and prevent lifestyle diseases.

PA has been considered health enhancing for decades, with health authorities advising that PA should be part of daily life throughout the whole lifespan.

Extensive changes in working environments have increased time spent on sedentary work and have a major impact on the accumulated PA profile and the related lifestyle diseases.

Muscular inactivity has been estimated to cause more than 1 million deaths annually in European countries.

This has even led experts to advise changes in classic ergonomic recommendations to focus on ways to increase the load and strain embedded in modern work activities.

The focus on inactivity as a health risk factor is not new. More than 300 years ago, Ramazzini suggested that,

“…those who sit at their work and are therefore called ‘chair workers’, should be advised to take physical exercise, at any rate on holidays. Let them make the best use they can of some one day, and so to some extent counteract the harm done by many days of sedentary life.”

However, claiming inactivity as an independent risk factor for poor health has led to an oversimplified disregard for the potentially detrimental effects of some forms of PA.

Although there is no doubt in the increased risk of overall low PA level for sedentary “chair workers,” there also is a concurrent risk of overloading, which Ramazzini also was aware of:

“The incessant driving of the pen over paper causes intense fatigue of the hand and the whole arm because of the continuous … strain on the muscles and tendons.”

In comparison with the increased focus in recent decades on cardiovascular mortality and longevity associated with sedentary jobs, much less attention has been paid to the equally important issue of musculoskeletal disorders (MSD), pain, and impaired function that has a major impact on prospects for living independently and with high quality of life

Muscle activity is not only beneficial for maintaining the muscles’ own capacity but also for maintaining the function of other organs and tissues.

Muscle is the main energy consumer posing a demand on the other body systems to provide the adequate energy delivery by regulating blood flow. Therefore, improving the capacity of the cardiovascular system is in general achieved by activating a large muscle mass dynamically at a high intensity. A significant increase in whole body energy turnover is additionally a key feature in prevention of obesity, metabolic syndrome, and diabetes.

Therefore, a compromised muscular function that impairs an active lifestyle with leisure time PA (LTPA) also may potentially increase the risk of common lifestyle diseases. It should be noted that the activity of only small muscle groups — as in light office work — will not sufficiently impact the cardiovascular system to attain a health effect.

PA takes place in different domains of daily life.

Over a lifespan, although the work domain counts for by far the largest share of the total energy expenditure during working days because of the large proportion of waking hours spent at work, this is seldom at a level that can promote fitness.

In contrast, sport and recreation count for only a minor share but nevertheless are the most important factors in prevention of lifestyle diseases

Figure 1
The daily profile of physical activity (PA) consists of the three domains of work, leisure time, and sleep alongside their subdivisions, each with its positive or negative contributions to effects on musculoskeletal health

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5473374/figure/F1/?report=objectonly

International recommendations for health-promoting PA do not distinguish between occupational PA (OPA) and LTPA as regards the effect of PA.

studies from recent cohorts undertaken this century, which have indicated distinct differences in health effects between LTPA and OPA.

The expected beneficial effect of LTPA was found as a decreased risk of cardiovascular disease among women and a decreased risk of cardiovascular death among men).

In contrast, high OPA was associated with a substantially increased risk.

This interactive effect is further supported by a study of sickness absence also showing negative effects of OPA and positive effects of LTPA. Similar effects also may be relevant for MSD, because the risk of repetitive, work-related strain injury has been found to be significantly reduced through high levels of LTPA.

LTPA is, in general, performed at the participants’ own discretion and may include training aimed at specific health-enhancing effects in relation to intensity, duration, or type of contraction. However, exaggeration of intensity or duration, as in elite sports, for example, may well lead to injuries.

The level, intensity, and duration of OPA are determined primarily by

• the demands of productivity,
• the purpose of the tasks, and
• the time allowed for certain productivity.

Such PA may well be health enhancing but only if maintained at moderation, as was already recognized as early as 1757 by the notorious royal physician, J.F. Struensee

The physical demands on muscle may be characterized by combinations of intensity and duration, which result in peak loads, static muscle activity, movements repeated for prolonged periods of time, or constrained postures.

These are all well-known risk factors in work-related MSD. (musculoskeletal disorder)

Epidemiological studies have shown distinctly different effects of OPA and LTPA, but the individual worker in daily life does not choose between the impact of physical exercise training and the occupational demands.

The challenge is rather to provide specific and intensive evidence-based training programs targeting the relevant body parts for the purpose of balancing those PA profiles that cause and cure muscular pain.

Figure 2
The model shows the counterbalancing effect of physical activity in terms of work and Intelligent Physical Exercise Training (IPET) on pain status and the additional side effects of IPET.

Novel Hypothesis

We propose the concept of “Intelligent Physical Exercise Training” (IPET), which aims to match and counterbalance the deteriorating impact of physical work demands including physical inactivity

This approach involves adjusting the profile of physical exercise training to match the impact of workload, including

• prolonged inactivity and overload, as well as
• the individual’s physical capacity and function.

Furthermore, both the localization and degree of muscular pain and relevant motivational factors should be considered.

PA AS CAUSE OF PAIN DEVELOPMENT AND MSD

MSD (musculoskeletal disorder) is a broad term covering any nonspecific disorder characterized by pain or decreased function and described as musculoskeletal trouble, ache, pain, or discomfort having a muscular, nervous, or arthritic origin.

MSD is highly prevalent and poses serious consequences for the individual as the most important cause of functional impairment.

inactivity and lack of strain infer a risk of tissue atrophy and degeneration, whereas excessive amounts of activity in terms of repetitions or intensities involve a risk of tissue damage mechanically or metabolically causing muscle pain and MSD.

In manual handling, the most commonly affected body regions are the hands, arms, and shoulder/neck. In jobs involving standing, walking, and lifting, the main areas affected are the lower back, hip, and knee.

There has been a global increase in sedentary jobs and a decrease in physically demanding jobs, but nevertheless, there has been a steady raise in MSD prevalence since early 1980s.

a job that from a cardiovascular perspective is inactive may from a muscular point of view present a risk of overload and exertion in specific body regions such as the small forearm and finger muscles.

The global increase in sedentary computer jobs and use of handheld digital devices also increase the need to maintain strenuous postures with static sustained contractions in the neck, shoulder, and wrist muscles and repetitive movements of the wrist and finger extensor muscles

Such tasks demand continuous low levels of muscle activity and are associated with high prevalence of pain in the neck, shoulders, and forearms.

The underlying risk factor in these tasks may be the long duration of sustained activation of specific motor units (MU) in the muscle, thereby eliciting muscular pain.

The inhomogeneous MU activation described previously during low-force sustained or repetitive contractions may create a localized increase in intramuscular pressure, which in turn may impede blood flow specifically to the locations of continuously active MUs belonging to the low threshold part of the motor neuron pool. This mismatch between use and delivery of oxygen with blood flow may disturb the aerobic energy turnover and result in more anaerobic processes.

Use of near-infrared spectroscopy technique during a 40-min standardized work task actually confirmed that oxygen availability initially showed a steep decrease and stayed low in the myalgic muscle, whereas during the same work task the oxygen availability in the healthy muscle gradually returned to baseline values. Furthermore, in this same 40-min low force repetitive work task, microdialysis revealed a local increase in the interstitial level of lactate and pyruvate both in healthy and myalgic muscles.

The myalgic trapezius muscle, however, despite similar blood flow as in the healthy muscle showed higher levels of these indicators of anaerobic metabolism, even in the baseline resting condition.

In addition to the differences in metabolically related substances, elevated concentrations of algesic substances were identified. The myalgic muscles in three different study populations showed higher levels of glutamate and serotonin than the normal muscle. These substance concentrations correlate with pain intensity and are associated with muscle cell damage and necrosis.

Taken together, myalgic muscles present adverse functional, metabolic, and morphological characteristics compared with healthy muscles both at rest and during a standardized repetitive task.

PA AS CURE FOR MUSCULAR PAIN AND HEALTH ENHANCEMENT

A review supports that ergonomic improvements or the use of tools such as biofeedback have limited effect on musculoskeletal health or even provide clear evidence of a lack of effect.

much less is known about a possible pain-reducing effect of physical exercise training and the morphological and biochemical mechanisms underlying a reduction in pain.

In a carefully planned randomized controlled trial (RCT) involving subjects with trapezius myalgia compared with matched healthy control subjects, we were able to show a number of differential beneficial effects of two types of exercise training: strength training and aerobic training.

Strength training was applied specifically to the neck and shoulder muscles. This initially acutely increased pain in the myalgic muscle after an exercise session, but over a 10-wk training period, a significant decrease was found. 

Regular daily training with hugely increased pain for 10 weeks – OUCH! This seems impossible to do except in these studies where they are forced.

Because pain causes (and is biologically intended to cause) avoidance, both physical and psychological, it becomes increasingly difficult to do activities that generate so much pain.

The aerobic exercise training caused a transient decrease in pain after each exercise session.

This is exactly the kind of exercise I’m trying to do, but I’m always limited by the burning pain in my muscles.

Furthermore, during a standardized repetitive work task, an improved blood flow and oxygenation as well as a reduced work-related pain were found after the 10-wk training period compared with baseline.

Any repetitive motion becomes excruciatingly painful for me. I’ve been bicycling for almost 4 decades and I’ve always had this problem, but it has become worse and worse until, these days, I can sometimes barely climb a flight of stairs.

The pain is so intense that I have to rest for a while halfway up and allow the pain to be cleared before I can continue. This situation makes it clear to me that the muscle burn is from lack of oxygen.

If I just wait long enough with the muscles relaxed they will become oxygenated again. Only then can I continue my exercise. Otherwise, the burn just gets worse and worse and without a limit.

TABLE (click for link to full-sized table)
Overview of positive results found in 17 RCT studies conducted at the workplace comprising more than 3500 workers with different job exposure