What’s on your recovery menu? (Part 2)
As a prelude to this month’s editorial, basic principles and application of emerging wearable devices was discussed in the May edition. The recovery challenge for athletes, is largely focussed on managing sustainable training loads and injury prevention.
Neuromuscular electrical stimulation therapy:
In a variety of forms, neuromuscular electrical stimulation therapy (NEST) has been around for decades. In an orthopaedic setting, NEST is useful during periods of limb immobilisation, such as accelerating quadriceps strength post- knee surgery (Gatewood et al, 2016). The application of NEST is quite simple: placing adhesive pads on or around the affected area and delivering a tolerable alternating electrical current, which stimulates muscle in order to mitigate pain and loss of muscle function.
Here we take a look at two commercially available NEST devices, Compex and Firefly, which are marketed to athletes. Firstly, we explore some scientific evidence, and secondly, highlight practical relevance to triathletes seeking to bolster their recovery.
A comprehensive review by Gondin and colleagues (2011), compiled key findings of research (up to 2010) investigating effects of electrical stimulation on post exercise recovery and performance in healthy individuals. Whilst each study was differing in design and protocol, a common theme emerged, which included an increase in maximal isometric strength following NEST. However gains in functional application (jumping, sprinting ability etc) were less clear unless NEST was also combined with a concurrent intervention, such as power or strength training.
A study by Gondin and colleagues (2005) investigated NEST effects on neural drive and muscle architecture. Twenty healthy males were divided into experimental (NEST = EXP) and control (CON) groups. Both groups underwent baseline, week 4, and week 8 measures of knee extensor maximal voluntary contraction (MVC) and electromyography (EMG = muscle electrical activity). The EXP group underwent 32 x 18min training sessions over 8 weeks, which included 40 isometric contractions during each session, with concurrent electrical stimulation (75Hz, 400 µs) via Compex portable device. After 8 weeks, key findings included a significant increase in MVC (27%); muscle activation (6%), quadriceps muscle cross sectional area (6%). The practical application from this study is consistent with previous research in this field; that electrical stimulation in the presence of voluntary isometric contractions, may benefit injury rehabilitation programs prior to, and during limb immobilisation.
A second study, by Billot and colleagues (2010) then went a step further, and explored NEST effects on performance parameters that have practical application on the sports field; in this case, strength, sprinting, jumping and kicking capacities of soccer players. Twenty male soccer players were allocated to EXP and CON groups, and completed baseline, week 3, and week 5 tests for strength, speed, power and ball speed. The EXP group underwent 3 x 12min NEST sessions per week for 5 weeks on knee extensors, including soccer training 5hrs per week. Whilst CON group completed only the same soccer training as EXP. NEST was delivered at 100Hz, 400 µs, via Compex portable device. After 5 weeks of NEST training, eccentric (22%), isometric (27%), and concentric (14-24%) torques and ball speed with and without run-up (5% and 9% respectively) had significantly improved. However, there was no improvement in sprint or power (jumping) performance. This study demonstrates that knee extensor muscle strength improved after only 3 weeks of NEST, which may compliment soccer specific tasks such as kicking. Sprinting and jumping involve complex interactions between multiple muscle groups, which may explain why there was no improvement found during these activities, given NEST was applied to only knee extensor muscles.
A third study by Warren and colleagues (2011), focussed their attention on blood lactate (BLA) and pitching speed responses to NEST. Seven male baseball players underwent a series of pitching 3 innings, and 3 different recovery methods (passive, active, NEST) over three days. Passive recovery meant no intervention for 6min; active recovery included light physical activity for 6min; NEST administered for 6min, at 9Hz, 250 µs, via Compex Sports Unit. Significantly lower BLA was found with NEST compared to active and passive recovery. NEST and passive recovery induced higher average pitching speed than active recovery, however NEST was no more effective than passive recovery.
The authors took the slant of increased BLA as a precursor to fatigue and performance inhabitation. Technically, this is not correct, as it is now well established that BLA is reflective of metabolic demand and adaptation, and is indeed an important source of fuel during intense exercise. In this study, lower BLA following NEST had no bearing on pitching performance compared to passive recovery. The mechanism for reduced BLA following NEST is equivocal, though likely due to increased blood flow, with subsequent re-distribution of lactate to inactive and previously active tissue.
Fire fly (elitesportrecovery.com.au)
Unlike the Compex device, the Firefly device is attached to skin across the peroneal nerve, behind the knee. Previous research by Tucker and colleagues (2010) demonstrated that peroneal nerve stimulation increases blood flow in the large femoral vein by up to 50-70% achieved when walking. Two studies in particular have recently investigated the effects of the Firefly device on muscle damage and soreness after exercise.
Ferguson and colleague (2014) compared the effects of NEST with compression garments and passive recovery (CON) on muscle strength, damage and soreness following endurance running. Twenty one healthy males completed a 90min shuttle running test on 3 separate occasions (each separated by 4 weeks), followed 1hr later by one of the 3 treatment. NEST was induced by Firefly (both legs for 12hrs, 1Hz, 70-560 µs); compression induced by graded compression socks (both legs for 12hrs, 40mmHg at the ankle, 20mmHg at calf). Passive recovery did not require any intervention. Perceived soreness increased for all groups after exercise, however less so in NEST compared to compression and CON after 24hr, and lower than CON after 48hr. There was no difference between treatments for isometric knee extensor strength. There was no difference between treatments for markers of muscle damage (CK, LDH), or inflammatory markers (IL-6, CRP). The authors recognised one limitation in the study included previous protective effects of muscle damage following the initial run test.
A second study by Taylor and colleagues (2015) investigated NEST effects on muscle power, speed, and muscle damage following intense training. Twenty eight male rugby and football players completed maximal speed training (6m x 50m; 5min recovery) on 2 separate occasions (each separated by 7 days), followed by NEST or CON. NEST was induced by Firefly (both legs for 8hrs, 1Hz, 140 µs); CON recovery did not require any intervention. Perceived soreness increased for all groups after exercise, however less so in NEST compared to CON after 24hr. Leg power decreased in both groups, however recovered more in the NEST groups after 24hr. Muscle damage marker CK increased in both groups, but was lower (better recovery) in NEST after 24hr. There was no difference between treatments for blood lactate, saliva testosterone and cortisol. The authors recognised that numerous recovery characteristics were apparent following NEST, but athletes should not expect to be fully recovered after 24hrs.
Considerations & take home message for triathletes
NEST certainly has its place in recovery following significant injury. There are also circumstances following heavy training and competition where NEST may be beneficial; however, not at the expense of fundamental recovery methods, including active movement, nutrition, sleep, etc. Both Compex and Firefly are easy to apply for time poor athletes, traveling, or have restricted access to other recovery modalities. When effective, the primary mechanism appears to be related to increased blood flow. The Firefly device may also elicit an effect on lymph flow, due to the specific low frequency of electrical signal, which typically results acceleration of muscle debris clearance. Chronic application of NEST, even though safe, is not recommended due to the probable loss of sensitivity to the treatment over time, and possible interference with muscle architecture adaptation and resilience to fatigue and damage.
Next edition we will focus attention to Part 3 of wearable recovery; including pneumatic compression and heart rate variability.
Dr Simon Sostaric
Exercise Physiologist / Sport Scientist
Dr Simon Sostaric is a distinguished exercise physiologist, sports scientist, researcher and author. Simon holds a physiology doctorate (Victoria University, Melbourne, Australia), in electrolyte regulation and skeletal muscle fatigue. He is the founder and director of Melbourne Sports & Allied Health Clinic (www.msahc.com.au), with 25 years’ experience in professional sport, clinical practice and academia.
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PHOTOGRAPHY: Compex And Firefly
Gatewood CT, et al (Knee Surg Sports Traumatol Arthrosc, 2016). The efficacy of post‑operative devices following knee arthroscopic surgery: a systematic review.
Gondin J, et al (Eur J Appl Physiol, 2011). Is high-frequency neuromuscular electrical stimulation a suitable tool for muscle performance improvement in both healthy humans and athletes?
Billot M, et al (J Strength & Cond Research, 2010). Effects of an electrostimulation training program on strength, jumping & kicking capacities in soccer players.
Gondin J, et al (Med Sci Sp & Ex, 2005). Electromyostimulation training effects on neural drive and muscle architecture
Warren C, et al (J Strength & Cond Research, 2011). Effect of three different between-inning recovery methods on baseball pitching performance.
Tucker A, et al (Int J Angiol, 2010). Augmentation of venous, arterial, and microvascular blood supply in the leg by isometric neuromuscular stimulation via peroneal nerve.
Ferguson R, et al (Eur J Appl Physiol, 2014). Neuromuscular electrical stimulation via the peroneal nerve is superior to graduated compression socks in reducing perceived muscle soreness following intense intermittent endurance exercise
Taylor T, et al (J Sc Sport Med, 2014). The impact of neuromuscular electrical stimulation on recovery after intensive, muscle damaging, maximal speed training in professional team sports players.