title: Pain duration is associated with increased muscle sympathetic nerve activity in patients with Achilles tendinopathy.
abstract: Tendinopathy is a common condition, which has been linked to surrogate measures of sympathetic nervous system (SNS) activity and insulin resistance. This study aimed to compare in vivo measures of the SNS and insulin resistance between individuals with and without Achilles tendinopathy. This case-control study compared Achilles tendinopathy sufferers to healthy controls. SNS activity was quantified using muscle sympathetic nerve activity (MSNA), while metabolic status was assessed via a modified glucose tolerance test and fasting lipid panel. Ultrasound tissue characterization assessed tendon structure. Resting MSNA did not differ between the 15 cases and 20 controls. Tendon pain duration in tendinopathy patients was correlated with burst frequency (R2=.32, P=.02) and burst incidence (R2=.41, P=.01) of MSNA. After adjusting for multiple comparisons, there was a trend suggesting fasting glucose was greater in cases (median 4.80, IQR .70 in cases vs 4.51, .38 in controls) and correlated with pain severity (R2=.14, P=.03), but no other metabolic measures were associated with tendon pain/structure. This study indicates that SNS activity is associated with tendon pain duration, building on previous data indicating the SNS is involved in recalcitrant tendinopathy. Metabolic parameters had little relationship with Achilles tendinopathy in this metabolically homogenous sample. Prospective studies are required to uncover the precise relationship between SNS activity, insulin resistance, and tendinopathy.
authors.affiliation: Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Vic., Australia.
authors.forename: J L
authors.initials: JL
authors.lastname: Jewson
authors.affiliation: Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Vic., Australia.|Department of Physiology, Monash University, Melbourne, Vic., Australia.
authors.forename: E A
authors.initials: EA
authors.lastname: Lambert
authors.affiliation: Department of Physiotherapy, Monash University, Melbourne, Vic., Australia.|Australian Centre for Research into Injury in Sport and its Prevention, Federation University, Ballarat, Vic., Australia.
authors.forename: S
authors.initials: S
authors.lastname: Docking
authors.affiliation: Department of Physiotherapy, Monash University, Melbourne, Vic., Australia.
authors.forename: M
authors.initials: M
authors.lastname: Storr
authors.affiliation: Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Vic., Australia.|Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Vic., Australia.
authors.forename: G W
authors.initials: GW
authors.lastname: Lambert
authors.affiliation: Department of Physiotherapy, Monash University, Melbourne, Vic., Australia.|University of Canberra Research Institute for Sport and Exercise (UC-RISE), Canberra, ACT, Australia.|Discipline of Physiotherapy, University of Canberra, Canberra, ACT, Australia.
authors.forename: J E
authors.initials: JE
authors.lastname: Gaida
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000503:physiopathology*; D000328:Adult; D016022:Case-Control Studies; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D010146:Pain / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D052256:Tendinopathy / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014463:Ultrasonography
keywords: 
  muscle sympathetic nerve activity
  ; Ultrasound tissue characterization; metabolic; tendons