October 2019

Objective assessment of stiffness in the gastrocnemius muscle in patients with symptomatic Achilles tendons

Authors: Gafin Morgan, Rhodri Martin, Helen Welch, Lisa Williams, Keith Morris

Affiliations: Podiatry & Orthopaedics, Cwm Taf Morgannwg University Health Board, Abercynon, UK; Biomedical Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom

Journal: Acta Kinesiologiae Universitatis Tartuensis BMJ Open Sport & Exercise Medicine - October 2019; 5:e000622 (DOI: 10.1136/bmjsem-2019-000622)

  • There was a significant decrease in gastrocnemius muscle tone and dynamic stiffness in the symptomatic Achilles tendon group.
  • Weight-bearing (WB) and non-weight-bearing (NWB) measurements demonstrated measurable differ- ences between symptomatic and asymptomatic tendons.
  • Significant differences in gastrocnemius stiffness of NWB and WB conditions suggest it is beneficial to measure both conditions.
  • The data observed may inform rehabilitation of the gastrocnemius muscle in patients with Achilles tendinopathy.

Objectives: To establish quantitative values of stiffness for the gastrocnemius muscle in patients diagnosed with Achilles tendinopathy.

Design: Case–control study with a single (cross sectional) time point of patients diagnosed with unilateral Achilles tendinopathy and an asymptomatic group.

Methods: Sample of 50 participants: 25 participants with symptomatic unilateral Achilles tendinopathy (symptomatic group) with the asymptomatic side of this group used as a control (control group 1). A third group of 25 participants with asymptomatic Achilles tendons (control group 2). Mechanical stiffness parameters, including natural oscillation frequency (F), dynamic stiffness (S), mechanical stress relaxation time (R), logarithmic decrement (D) and creep (C), were assessed using the MyotonPRO. Measurements at the medial and lateral gastrocnemii were taken as non-weight bearing (NWB) and weight bearing (WB).

Results: Significant (p<0.05) differences were observed between the mean symptomatic group and control groups 1 and 2 in the WB and NWB conditions for natural oscillation frequency (F), dynamic stiffness (S), and creep (C). There was a significant reduction in S WB and conversely a significant increase in S of the symptomatic group NWB. Creep (C) and mechanical stress relaxation time (R) were significantly (p<0.05) less in the symptomatic group NWB. Significant differences were observed between the NWB and WB data sets for logarithmic decrement (D). NWB D demonstrated significantly (p<0.05) higher scores than the WB condition.

This study demonstrated that there was a significant reduction in stiffness of the gastrocnemius muscle in participants with Achilles tendinopathy compared with the two control groups. The WB MyotonPRO measures for the symptomatic group of F and S were significantly lower, indicating a decrease in the tonal properties (F) and the dynamic stiffness (S) of the muscle. Our data demonstrated that women presented with increased stiffness in the symptomatic group. The application of MyotonPRO technology to measure changes in stiffness in the gastrocnemius muscle may be useful to measure as part of a rehabilitation programme where specific attention could be placed to increase the tonal properties of the muscle. Further studies are required to develop a robust clinical application of this technology, particularly with regard to Achilles tendinopathy.