Mervyn Travers

Achilles tendinopathy alters stretch shortening cycle behaviour during a sub-maximal hopping task

OBJECTIVES To describe stretch shortening cycle behaviour of the ankle and lower limb in patients with Achilles tendinopathy (AT) and establish differences with healthy volunteers. DESIGN Between-subjects case-controlled. METHODS Fifteen patients with AT (mean age 41.2±12.7 years) and 11 healthy volunteers (CON) (mean age 23.2±6.7 years) performed sub-maximal single-limb hopping on a custom built sledge-jump system. Using 3D motion analysis and surface EMG, temporal kinematic (lower limb stiffness, ankle angle at 80ms pre-contact, ankle angle at contact, peak ankle angle, ankle stretch amplitude) and EMG measures (onset, offset and peak times relative to contact) were captured. Data between AT and CON were compared statistically using a linear mixed model. RESULTS Patients with AT exhibited significantly increased lower limb stiffness when compared to healthy volunteers (p<0.001) and their hopping range was shifted towards a more dorsiflexed position (p<0.001). Furthermore, ankle stretch amplitude was greater in AT compared with healthy volunteers (p<0.001). A delay in muscle activity was also observed; soleus onset (p<0.001), tibialis anterior peak (p=0.026) and tibialis anterior offset (p<0.001) were all delayed in AT compared with CON. CONCLUSIONS These findings indicate that patients with AT exhibit altered stretch-shortening cycle behaviour during sub-maximal hopping when compared with healthy volunteers. Patients with AT hop with greater lower limb stiffness, in a greater degree of ankle dorsiflexion and have a greater stretch amplitude. Likewise, delayed muscle activity is evident. These findings have implications in terms of informing the understanding of the pathoaetiology and management of AT.

Eccentric fatigue modulates stretch-shortening cycle effectiveness - a possible role in lower limb overuse injuries

The role of fatigue in injury development is an important consideration for clinicians. In particular, the role of eccentric fatigue in stretch-shortening cycle (SSC) activities may be linked to lower limb overuse conditions. The purpose of this study was to explore the influence of ankle plantarflexor eccentric fatigue on SSC effectiveness during a hopping task in healthy volunteers. 11 healthy volunteers (23.2±6.7 years) performed a sub-maximal hopping task on a custom-built sledge system. 3D motion capture and surface EMG were utilised to measure lower limb stiffness, temporal kinematic measures and muscle timing measures at baseline and immediately following an eccentric fatigue protocol. A linear mixed model was used to test whether measures differed between conditions. Compared to baseline, eccentric fatigue induced increased stiffness during the hopping task (+ 15.3%; P<0.001). Furthermore, ankle stretch amplitude decreased (- 9.1%; P<0.001), whilst all other ankle kinematic measures remained unchanged. These changes were accompanied by a temporal shift in onset of activity in soleus and tibialis anterior muscles (- 4.6 to - 8.5%; p<0.001). These findings indicate that eccentric fatigue alters SSC effectiveness in healthy volunteers. These findings may be applied to inform pathogenetic models of overuse injury development.

Commentary: Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain

It was with great interest we read the recently published article “Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain.” Investigating back pain (BP) in adolescents is commendable as there is growing evidence that for many, an experience of BP as early as 14 years of age may relate to ongoing pain in adulthood (Coenen et al., 2017). Indeed, the conventional narrative is changing as individual physical factors such as posture, use of schoolbags, and hypermobility are only weakly associated with adolescent BP. Rather, factors which predict BP at a young age are considered to be multi-dimensional and include gender, negative BP beliefs and poor mental health (O’Sullivan et al., 2017; Smith et al., 2017). Mueller et al. (2017) have focused on a single physical factor (trunk muscle activation patterns) drawing inferences regarding BP prevention and treatment. This article prompts consideration of three essential aspects regarding research design and interpretation of findings:

Exercise-induced hypoalgesia in women with varying levels of menstrual pain

Abstract Background and aims: Exercise-induced hypoalgesia (EIH) is a well-established phenomenon in pain-free individuals that describes a decrease in pain sensitivity after an acute bout of exercise. The EIH response has been demonstrated to be sub-optimal in the presence of persisting pain. Menstrual pain is a common recurrent painful problem with many women experiencing high levels of pain each cycle. However, the EIH response has not been examined in a cohort of women with high levels of menstrual pain. This research aimed to examine whether EIH manifests differently in women with varying levels of menstrual pain. The primary hypothesis was that women with high levels of menstrual pain would demonstrate compromised EIH. Secondary aims were to explore relationships between EIH and emotional state, sleep quality, body mass index (BMI) or physical activity levels. Methods: Pressure pain thresholds (PPT) were measured in 64 participants using a digital handheld algometer before and after a submaximal isometric-handgrip exercise. EIH index was compared between low (VAS 0–3), moderate (VAS 4–7) and high (VAS 8–10) pain groups, using a linear mixed model analysis with participant as a random effect, and site, menstrual pain category and the interaction between the two, as fixed effects. Results: EIH was consistently induced in all groups. However, there was no statistically significant difference between the pain groups for EIH index (p=0.835) or for any co-variates (p>0.05). Conclusions: EIH was not found to differ between women who report regular low, moderate or high levels of menstrual pain, when measured at a point in their menstrual cycle when they are pain free. Implications: This study provides insight that EIH does not vary in women with differing levels of menstrual pain when they are not currently experiencing pain. The current findings indicate that, although menstrual pain can involve regular episodes of high pain levels, it may not be associated with the same central nervous system dysfunctions as seen in sustained chronic pain conditions.

Visually-induced analgesia in a deep tissue experimental pain model: A randomised cross-over experiment

Visualizing ones own painful body part appears to have an effect on reported pain intensity. Furthermore, it seems that manipulating the size of the viewed image can determine the direction and extent of this phenomenon. When visual distortion has been applied to clinical populations, the analgesic effects have been in opposition to those observed in some experimental pain models. To help resolve this problem, we explored the effect of visualisation and magnification of the visual image on reported pain using a delayed onset muscle soreness (DOMS) pain model.

28 Eccentric Fatigue Alters Stretch-shortening Cycle Behaviour During A Sub-maximal Hopping Task

Introduction Achilles tendinopathy is believed to be driven in part by eccentric fatigue.1 Likewise, interventions that improve resilience to eccentric fatigue demonstrate efficacy.2 An experimental model of eccentric fatigue has the potential to inform our understanding of the underlying operating mechanisms. The purpose of this study was therefore to explore the influence of a longitudinal experimental model of eccentric fatigue on stretch shortening cycle behaviour during a sub maximal hopping task in healthy volunteers. In doing so, our understanding of the role that fatigue, pain and structural changes play in the development and rehabilitation of Achilles tendinopathy may be progressed. Methods Eleven healthy volunteers (23.2 ± 6.7 years) performed a sub-maximal hopping task on a custom-built sledge system. A 3D motion capture system and surface EMG was utilised to measure temporal kinematic measures (lower limb stiffness, ankle angle 80 ms pre-contact, ankle angle at contact, peak ankle angle, ankle stretch amplitude) and muscle timing measures (soleus and tibialis anterior onset, peak and offset), respectively over 4 testing occasions; baseline, acute fatigue (5 min), pain (2 days) and recovered (7 days). Results Compared to baseline, volunteers hopped with greater stiffness in all experimental conditions (p < 0.001). Stiffness increased in fatigue and again in pain, before partially returning in the recovered state (Figure 1). Compared with baseline, when fatigued, participants ankle kinematics were unchanged; however in pain, participants hopped in greater dorsiflexion (p < 0.001) but had reduced stretch amplitude (Figures 1 and 2). Once recovered, ankle kinematics returned towards baseline levels, albeit shifted towards a more plantarflexed position (p < 0.001). Soleus activity became earlier in each experimental condition, whilst tibialis anterior activity also became earlier in each experimental condition, except in the recovered state where it became relatively delayed. Abstract 28 Figure 1 Stretch amplitude and stiffness Abstract 28 Figure 2 Ankle Kinematics (° plantarflexion) Discussion These findings indicate that experimentally induced fatigue alters stretch-shortening cycle behaviour in healthy volunteers. Likewise, the structural changes that occur following such an intervention also lead to alterations in behaviour. Specifically, lower limb stiffness increases, ankle kinematics shift towards a more plantarflexed position, and muscle activity becomes earlier. These findings have clinical applications supporting theoretical models of the pathoaetiology of Achilles tendinopathy and the mechanisms underpinning eccentric loading interventions. References 1 Shepherd, et al. Int J Exp Path. 94:260–270 2 Magnuson, et al. Clin J Sports Med. 19:54–64