A retrospective study of isokinetic dynamometry parameters in patients diagnosed with unilateral Achilles tendinopathy

Abstract

Introduction: The Achilles tendon, the strongest tendon in the human body, is vital for locomotive activities like walking and running. Despite its strength, it is prone to Achilles tendinopathy (AT), a debilitating condition characterised by pain, swelling, and decreased performance. As a common foot and ankle disorder, AT’s prevalence spans across athletes, recreational exercisers, and the sedentary population, with incidences up to 52% in former elite athletes with a lifetime incidence of six percent in the general population. The aetiology of AT involves both extrinsic- and intrinsic risk factors, including overuse, biomechanical irregularities, and muscular dysfunction, particularly in the gastrocnemius-soleus muscles. Research indicates that plantar flexor weakness often occurs before Achilles tendon pain develops. Weakness in the plantar flexor muscles is a key modifiable risk factor for AT issues. Conventional research on AT has primarily focused on peak torque (PT) derived from isokinetic dynamometry evaluations, leaving a gap in understanding the full spectrum of muscle performance affected by AT. Isokinetic dynamometry, with its versatile protocols and advanced software, can comprehensively evaluate muscle performance from both strength and endurance perspectives, addressing this gap. Aim of study: This study aimed to investigate the effects of unilateral AT on various isokinetic dynamometry parameters, including torque, position, and time, in individuals diagnosed with this condition. The objectives were to determine the extent of dysfunction and weakness in the gastrocnemius-soleus muscles and to compare these parameters between symptomatic and asymptomatic extremities, thus enhancing the understanding of AT's unilateral nature. By expanding the analysis beyond PT, the study addresses the gap in current research, exploring a more comprehensive scope of muscle performance in AT. Method: This retrospective study investigated the impact of unilateral AT on isokinetic dynamometry parameters. Participants were males and females, aged 18 years or older, diagnosed with unilateral AT. Initial isokinetic dynamometry evaluation reports from 2015 to 2022 were collected from a private biokinetics practice in South Africa. Although data on 54 participants initially met the inclusion criteria, the exclusion criteria, which required evaluations to be performed at an angular velocity of 60 degrees per second, reduced the number of suitable reports. Consequently, only the evaluations of n=21 participants (n=18 males and n=3 females, with a total sample mean age of 53.1 years) were included in the study. Isokinetic dynamometry evaluation, conducted by registered biokineticists, followed standardised protocols with the Humac Norm Cybex Testing and Rehabilitation System. Parameters analysed included torque, position, and time measures. Statistical analysis 4 involved paired t-Tests and Wilcoxon tests for normally and non-normally distributed data, respectively, with a significance level set at p<0.05. Results: The analysis of PT between symptomatic- and asymptomatic extremities revealed no statistically significant difference, with symptomatic extremities demonstrating a mean PT of 38.81 foot-pounds (SD: ±10.97) compared to 40.91 foot-pounds (SD: ±11.48) for asymptomatic extremities (p = 0.24). However, a significant difference was noted in the joint angle at PT (JAPT), as determined by the Wilcoxon signed-rank test. Symptomatic extremities exhibited a lower mean joint angle of 1.8 degrees (SD: ±5.11) compared to 2.24 degrees (SD: ±3.89) in asymptomatic extremities (p = 0.0001). Time to PT (TPT) did not differ significantly between symptomatic- (0.20 seconds; SD: ±0.13) and asymptomatic (0.21 seconds; SD: ±0.11) extremities (p = 0.16). Similarly, time PT held (TPTH) showed no significant difference between symptomatic- (0.36 seconds; SD: ±0.33) and asymptomatic (0.34 seconds; SD: ±0.39) extremities (p = 0.49). The analysis of work per repetition (WPR) revealed marginal differences between symptomatic- (17.57 foot-pounds; SD: ±5.48) and asymptomatic (18.91 foot-pounds; SD: ±5.90) extremities, but these differences did not reach statistical significance (p = 0.16). The average power per repetition (APR) differed between symptomatic- (35.48 watts; SD: ±11.71) and asymptomatic (39.05 watts; SD: ±13.14) extremities, with a paired t-Test indicating a trend toward statistical significance (p = 0.06), though this did not meet the conventional threshold for significance in this sample. Conclusion: The study provides an understanding of unilateral AT's impact on isokinetic dynamometry parameters. The study highlighted bilateral muscle dysfunction and weakness in individuals with unilateral AT. This was evidenced through the comparative analysis of PT, PT percentage body weight (PT%BW) and PT ratio (PTR) parameters against established norms. Achilles tendinopathy does not significantly affect the speed of muscle contraction or endurance in maintaining PT. This questions the notion of unilateral impairment in AT and highlights the necessity of a comprehensive approach in rehabilitation, focusing on strength, endurance, and biomechanics. The findings also suggest the need for further research with larger cohorts and varied isokinetic dynamometry parameters to validate these conclusions and enhance rehabilitation protocols in AT.