Using near-infrared spectroscopy (NIRS) and the tracer indocyanine green (ICG), we quantified blood flow in calf muscle and around the Achilles tendon during plantar flexion (1-9 W). For comparison, blood flow in calf muscle was determined by dye dilution in combination with magnetic resonance imaging measures of muscle volume, and, for the peritendon region, blood flow was measured by (133)Xe washout. From rest to a peak load of 9 W, NIRS-ICG blood flow in calf muscle increased from 2.4+/-0.2 to 74+/-5 ml x 100 ml tissue(-1) x min(-1), similar to that measured by reverse dye (77+/-6 ml x 100 ml tissue(-1) x min(-1)). Achilles peritendon blood flow measured by NIRS-ICG rose with exercise from 2.2+/-0.5 to 15.1+/-0.2 ml x 100 ml(-1) x min(-1), which was similar to that determined by (133)Xe washout (2.0+/-0.6 to 14.6+/-0.3 ml x 100 ml tissue(-1) x min(-1)). This is the first study using NIRS and ICG to quantify regional tissue blood flow during exercise in humans. Due to its high spatial and temporal resolution, the technique may be useful for determining regional blood flow distribution and regulation during exercise in humans.

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Background Tendinopathies of the lower extremity (e.g. Achilles, patellar, and plantar heel pain) are common in both general and sporting populations. However, the prevalence and incidence in Danish general practice is unknown. The aim was to determine the prevalence and incidence rate of lower-extremity tendinopathies in a Danish general practice. Methods In this registry-based study, we extracted data from the electronic patient files of all patients in a single Danish general practice. The practice included 8836 patients. We searched ICPC-2 codes to identify patients with either of the following lower-extremity tendinopathies: plantar heel pain; Achilles tendinopathy; patellar tendinopathy; greater trochanteric pain syndrome or adductor tendinopathy. We defined an incident and prevalent case as a patient with a consultation because of tendinopathy in 2016 only. A prevalent, but not incident case was a patient with consultations in both 2015 and 2016. Incidence and prevalence were expressed as the number of patients with a tendinopathy per 1000 registered patients. Results The prevalence and incidence rate were 16.6 and 7.9 per 1000 registered patients, respectively. Plantar heel pain was the most prevalent tendinopathy and accounted for 39% of lower-extremity tendinopathies. Patients with tendinopathies were significantly older than all registered patients (46.0 years (95%CI: 43.3;48.7) versus 38.8 years (95%CI: 38.4;39.3), respectively). Conclusions Lower-extremity tendinopathies, especially plantar heel pain, had a high prevalence and incidence rate in a Danish general practice. In a typical general practice with 5000 patients, general practitioners should expect to see more than 80 patients with a lower-extremity tendinopathy every year.

ObjectivesInvestigate the prognosis of adolescent knee pain, and evaluate its impact on health, care-seeking and career choices 5 years later.DesignPre-registered, prospective cohort study.SettingPopulation-based cohort initiated in school setting.ParticipantsFrom a cohort of 2200 adolescents aged 15–19 years in 2011, 504 reported knee pain on at least a monthly basis, and were followed prospectively in this cohort study, together with 252 controls who did not have knee pain in 2011.Main outcome measuresOutcomes included the Pain and Symptoms subscales from the Knee injury and Osteoarthritis Outcome Score (KOOS), pain intensity measured with a Numeric Rating Scale, pain frequency, knee-related and health-related quality of life, sports participation, physical activity level, KOOS subscales: Function and Sport/recreation, quality of sleep, healthcare consultations, treatments received for their knee pain, the use of painkillers and impact on choice of job or career.ResultsAt follow-up, 358 (71.0%) from the knee pain group and 182 (72.2%) from the control group responded. Of note, 40.5% (95% CI: 35.4% to 45.6%) from the knee pain group reported knee pain 5 years later which was frequent and intense compared with 13.2% (95% CI: 8.2 to 18.1) of the control group. Those from the knee pain group still suffering from knee pain reported poorer physical health (13 points worse on KOOS Function and 30 points worse on KOOS Sport/recreation), stopped or reduced their sports participation because of knee pain (60%), reported worse sleep quality and worse knee-related and general quality of life. In terms of health behaviours, those still with knee pain reported more healthcare consultations. One-third used pain killers regularly, and 15% (95% CI: 12% to 20%) reported that knee pain influenced their choice of job or career.ConclusionFour out of every 10 adolescents with knee pain still experienced frequent and intense knee pain 5 years later, severe enough to impact health, health behaviours and career choices.Trail registration numberNCT02873143.

Background: Patellofemoral pain (PFP) and Osgood Schlatter (OSD) are common in adolescents, but we lack knowledge on these conditions and their impact in young adolescents (<15 years).Objectives: Compare pain, physical activity, quality of life, strength and knee function between adolescents with PFP or OSD, compared to pain-free controls. Methods: Self-report questionnaires were used to describe pain, physical activity, knee function, and quality of life in participants with PFP (N=151), OSD (N=51), and pain-free controls (N=50) aged between 10 and 14 years. Hip and knee strength were measured by handheld dynamometry.Physical activity levels were measured using wearable accelerometers.Results: More than 98% with PFP or OSD participated in sports prior to knee pain, and 60% reported reduced sports participation due to pain. Despite this, the adolescents were highly active (accumulating >120min vigorous physical activity per day), with no differences between OSD, PFP, or controls.Adolescents with knee pain (PFP and OSD) scored 23-57 points lower than controls (P<0.001) in the Knee Osteoarthritis Outcome Score. Adolescents with OSD had lower knee extension strength compared to controls (P<0.05, effect size (ES) 1.25). In the PFP group, only females displayed lower hip abduction strength compared to female controls (P<0.05, ES 0.49). Both girls and boys with PFP had lower hip extension strength compared to controls (P<0.05, ES 0.73). Conclusion:Adolescents with PFP or OSD are characterized by high physical activity levels, despite impaired sports participation and knee function relative to pain-free controls.

Brain. 2002 Feb;125(Pt 2):320‐326 Painful impulses from tender pericranial muscles may play a major role in the pathophysiology of chronic tension‐type headache. Firm evidence for peripheral muscle pathology as a cause of muscle pain and chronic headache is still lacking. Using a microdialysis technique, we aimed to estimate in vivo blood flow and interstitial lactate concentrations in the trapezius muscle at rest and during static exercise in patients with chronic tension‐type headache and in healthy subjects. We recruited 16 patients with chronic tension‐type headache and 17 healthy control subjects. Two microdialysis catheters were inserted into the trapezius muscle (on the non‐dominant side) of subjects, and dialysates were collected at rest, 15 and 30 min after the start of static exercise (10% of maximal force) and 15 and 30 min after the exercise was completed. All samples were coded and analysed blind. The primary endpoints were to detect a difference between patients and controls in changes of muscle blood flow and the interstitial lactate concentration from baseline to exercise and post‐exercise periods. The increase in muscle blood flow from baseline to exercise and post‐exercise periods was significantly lower in patients than controls (P  =  0.03). There was no difference in resting blood flow between patients and controls (P  =  0.43). Resting interstitial concentration of lactate did not differ between patients (2.51  ± *T0.18 mM; mean ± standard error of the mean) and controls (2.35  ±  0.23 mM, P  =  0.57). There was no difference in change in interstitial lactate from baseline to exercise and post‐exercise periods between patients and controls (P  =  0.38). The present study provides in vivo evidence of decreased blood flow in response to static exercise in a tender muscle in patients with chronic tension‐type headache. We suggest that, because of increased excitability of neurones in the CNS, the central interpretation and response to normal sensory input are altered in patients with chronic tension‐type headache. This may lead to enhanced sympathetically mediated vasoconstriction and thereby a decreased blood flow in response to static exercise. Comment: An important study which links decreased blood flow in statically exercised trapezius muscle in patients with chronic tension‐type headache (CTTH) with muscle tenderness. A better understanding of the pathophysiology of CTTH may provide a clue to novel therapeutic maneuvers. DSM

Isometric exercise is commonly recommended for immediate pain relief in individuals suffering from lower limb tendinopathies, despite the limited evidence supporting its analgesic effect. Due to the similarities between plantar fasciopathy and tendinopathies, the aim of this trial was to investigate the acute effect of isometric exercise on pain, compared to isotonic exercise, or walking, in individuals with plantar fasciopathy. We recruited 20 individuals with plantar fasciopathy for this prospectively-registered, participant-blinded, randomized, superiority crossover trial (ClinicalTrials.gov: NCT03264729). Participants attended three exercise sessions (isometric, isotonic, or walking) in a randomized order, within a 2-week period. Both isometric and isotonic exercises were performed standing with the forefoot on a step bench, while walking was performed barefoot. The primary outcome was pain (measured on a 0-100-mm VAS) during a pain-aggravating activity. Secondary outcomes included pressure pain threshold (PPT) under the heel, and plantar fascia thickness (PFT). All outcomes were measured before and after each exercise session. There were no significant differences between the three exercises on pain (P = 0.753), PPTs (P = 0.837), or PFT (P = 0.718). Further, there was no change in pain from before to after any of the exercises (isometric exercise 2.7 mm [95% CI: -12.2; 6.8], isotonic exercise -3.4 mm [95% CI: -5.0; 11.8], or walking 1.6 mm [95% CI: -16.1; 12.9]). Contrary to expectations, isometric exercise was no better than isotonic exercise or walking at reducing pain in individuals with plantar fasciopathy. None of the exercises induced any systematic analgesic effect.

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