Sunday, 6 April 2014

Novel Uses of Accommodating Resistance in Hip and Spine Extensor Training

Everybody loves a pert posterior. Not only that, but trainees interested in more than turning heads alone can have much to benefit from intelligent training of the hip and spine extensors when it comes to physical performance in numerous activities and sports.

We’re all familiar with barbell hip extension exercises such as the Deadlift and Good Morning, movements which have earned the high esteem in which so many people hold them; however, this doesn’t mean that a few minor tweaks to such exercises can’t improve them. This brings us to the crux of today’s article: how can we tweak conventional barbell hip extension exercises to overcome their shortcomings and thereby elicit new-found progress?

While many people around the world have probably used some of the exercises we’ll cover today, I’d like to give credit to coach Stuart McMillan as it was he who gave me the idea to try using bands in the manner outlined in this article.


Who are these Exercises for?

While these exercises can be used by anybody with access to the requisite equipment, I’d reserve them largely for highly-experienced physique athletes looking for a novel training stimulus or athletes competing in sports in which improved hip extensor strength qualities throughout their available hip flexion range of motion are sought. In this instance these are particularly effective as stand-alone exercises for this reason. This can be very useful during a competitive period as at this time the athlete is likely to include reduced volumes of a smaller variety of exercises than during general or specific preparatory periods (i.e. the off-season). Including exercises such as these that can potentially recruit a larger number of motor units than their conventional counterparts and thereby reduce the volumes of strength training necessary to retain strength qualities. This strategy can also be used to particularly good effect by Powerlifters seeking improved hip extensor contribution and strength near the ‘lockout’ in the Deadlift and Squat.

Needless to say, many of these exercises do require a little more time than most to set up and may need some practice before an optimal equipment set-up is realised. This means that they’re probably not suited to those with very tight schedules or the attention spans of goldfish. Likewise, even in facilities with the necessary equipment, implementing these exercises when training in groups can be tedious if the trainees are of very different heights or strength levels.


Traditional Hip Extension Exercises: Basic Biomechanical Barriers

Many stimuli can serve to initiate increased muscle fibre volume and strength. Lengthening of muscle-tendon units under loads is particularly effective at inducing microtrauma of the muscles resisting this load (Clarkson & Hubal, 2002). The ensuing exercise-induced muscle damage appears to contribute to muscle re-modelling via multiple mechanisms including activation and proliferation of satellite cells, stem and progenitor cells that are essential to skeletal muscle growth (Wang & Rudnicki, 2011). Therefore, selecting exercises in which the torque at a given joint is highest when the target muscle fibres are near the limits of your flexibility, as per exercises such as Good Mornings and Romanian Deadlifts, can be an effective stimulus in initiating muscle hypertrophy. The trouble with these exercises is that as the muscles in question return to the start position their activity diminishes given the reduction in hip extension torque. The product is an exercise that is not highly demanding throughout its range of motion.

Exercises such as Pull-Throughs entail a different direction of force to the axial loading evident in Good Mornings and Romanian Deadlifts as the pulley passes rearwards between the legs; however, many find them cumbersome and they are unlikely to reach the demands that exercises like Good Mornings and Romanian Deadlifts can create when the hip extensors are at their longest. Furthermore, Pull-Through loading can be limited by the mass of the weight stack as the individual’s strength increases. Other exercises such as the 45-Degree ‘Back’ Extension are also effective and require relatively high hip extension torques throughout the range of motion, although again these probably do not load the hip extensors as greatly in the stretched position as their barbell counterparts.

Finally, flexed-knee hip extension exercises such as Hip Thrusts are undoubtedly great exercises for a shapely behind. However, such exercises cannot rival other hip extension exercises with respect to hamstring recruitment and for those seeking exercises that are specific to developing hip extensor power in sports played in standing, exercises such as Hip Thrusts arguably have less dynamic correspondence to some of the standing exercises that I will detail in this article.


Accommodating Resistance: more than a Band-aid

So-called ‘accommodating resistance’ comes in a number of guises, including bands, chains and weight-releasers. Traditionally these have been used to modify barbell exercises characterised by axial loading in which force acts along the line of an axis. An example of this would be seen in the spine during a Squat with a barbell as the load compresses the spine vertically.

Exercises such as Good Mornings have an ascending strength curve as the individual is weaker at greater lengths of the agonist musculature (in the bottom of a Squat, for example) and higher loads can be lifted as the limbs are increasingly extended. Therefore, the use of accommodating resistance providing resistance vertically downwards can be very helpful for those interesting in flattening a largely ascending strength curve and thereby increasing the demands on the target musculature throughout the exercise. This is not only of interest to Powerlifters as physique athletes should seek to maximise the demands on the target musculature throughout an exercise’s range of motion as many by-products of anaerobic metabolism are implicated in eliciting muscle hypertrophy.

Using accommodating resistance in this manner can therefore undoubtedly be useful in certain circumstances. Nonetheless, it can also be helpful to manipulate the direction of the resistive force in order to better target certain muscles. For example, the application of a force to the hips that attempts to pull them rearwards while standing upright would necessitate increased hip extensor activity to prevent the hips from flexing. When a weighted implement such as a barbell is then introduced too, the result is an exercise akin to a hybrid between the traditional standing exercise and the Hip Thrust.


The Meat of the Matter: Great Glutes and Huge Hamstrings

Using bands in the way I’ll outline below can be applied to any standing exercise that requires significant hip extension, so please don’t feel limited to the examples that I’ll outline. That being said, because that bands exert a force that must be resisted in order to maintain balance, the exercises detailed are either symmetrical or split stance movements requiring lower limb bilateral force contribution; unilateral exercises can be used if you wish to train your balance, but I’d suggest that these are generally awkward and inferior in developing outcomes like muscle hypertrophy and maximal strength development.


Band Placement and Resistance

The bands should be secured at around waist level a few feet behind where you’ll be lifting the implement (e.g. barbell). Next, step inside the band and lift it such that it wraps around the front of the hips just above the crown jewels. Step forward towards the implement ensuring that the band remains placed appropriately and, once happy with the set-up, begin the exercise. With respect to band resistance, I’d suggest beginning with a relatively extensible band; you can always progress to a stronger band as you develop proficiency in the exercises. As the resistance offered by a band increases as it is extended, it is important to be meticulous about band placement each time you incorporate the exercises.


Deadlift Variations

Bands can be used in this manner with any Deadlift of your choice, including Dumbbell, Barbell, Kettlebell, and Trap bar variations. The following images are of the Romanian Deadlift:



Likewise, the range of motion of these exercises can be tweaked; the range can be increased by standing on a sturdy box or reduced by elevating the implement or simply deliberately curtailing the range of motion. Furthermore, the demands on the hip extensors during the lowering portion of these exercises can be increased by accentuating this phase (performing it with more extended knees than the lifting portion).



At the bottom of the exercise, push your knees forwards to the position below.



Finally, return to the starting position.

Bonus Exercise: Split Stance Deadlifts

One oft-overlooked Deadlift variation that may be of interest to some athletes is the Split Stance Romanian Deadlift. In this exercise, the feet are hip-width apart and slightly staggered such that the toes of the rearward foot are level with the heel of the forward foot. The heel of the rear foot remains slightly off the floor throughout the exercise and the purpose of this rear leg is primarily to provide balance as the forward leg contributes the majority of the work performed. The exercise itself then adheres to the same principles as the conventional Romanian Deadlift and can of course be performed with a variety of implements.
  


If you try this exercise, just ensure that the knee of the forward leg tracks in line with the centre of the toes of that leg and that the rear foot points forward throughout. Begin with light loads and reinforce good technique and a pronounced stretch through the hip extensors as you descend. You can shift the emphasis away from the hamstrings to the Gluteus Maximus by flexing the knees more during the descent and thereby mimicking the conventional Deadlift. This exercise can of course also be performed using bands, as described.

Good Morning Variations

Once again, a multitude of Good Morning variations can be used. The same technical considerations apply as per its Romanian counterpart.



Bonus Exercise: Split Stance Good Mornings

In this exercise the foot placement is as described above in the Split Stance Deadlift.



This exercise can of course also be performed using bands, as described.



Squat Variations

Any bilateral Squat can be used to good effect here; I’d suggest that Single-Leg Squat and Split Squat exercises are less suited to this method. The following photos are of the Back Squat:





Bonus Exercise: Hamstring Squat

One novel barbell squat that you may wish to try if you’re keen to target your hamstrings is a kind of Good Morning/Squat hybrid. After unracking the bar, squat down as is typical.

                              

As you ascend keep your hips flexed such that the top of the exercise now mimics that the bottom position of the Good Morning. Viewed from the side, the angle of your back would therefore remain relatively constant throughout the exercise.


I’d not that this particular exercise does not really lend itself to using bands as described in this article as the hips remain flexed throughout.


Exercise Progressions and Further Modifications

The exercises can be progressed in all of the usual ways (i.e. increased bar mass, bar velocity, range of motion, work performed, work performed per unit of time, etc). However, where bands are used, band resistance can also be increased by either stretching the same band more by standing further from its anchor points or selecting a stronger band. Increasing the band resistance will generally require a higher relative contribution of the Gluteus Maximus, specifically.

As an alternative to bands, a pulley with a waist harness attachment can be used to achieve a similar outcome. The primary difference between the bands and the pulley will be that resistance from the bands increases as the individual stands up from hip flexion, whereas the resistance offered by the pulley will remain roughly constant throughout.

These exercises can also all be performed with accommodating resistance used in the traditional manner as well as this method; chains could be draped around the barbell too, for example. This way you’ll both flatten the strength curve during such exercises in addition to enhancing Gluteus Maximus recruitment. The only drawbacks are the time taken to set up the exercises and some inevitably strange looks that may come your way!

Finally, some of these exercises could be performed as mechanical drop sets; for example, you could perform the Good Morning/Squat hybrid until near fatigue and then continue with the conventional Squat to extend the set. Likewise, you can perform exercises with bands until near fatigue and then remove the bands and thereby extend the set.


Closing Thoughts

Many athletes and physique athletes alike may have much to gain from some of these exercises. If it has not already done so, I’m sure it will dawn on you the methods outlined in this article can be applied to a near-endless variety of exercises; you are only limited by your imagination and can always strive for more effective training methods. Give these exercises an honest go if your gym permits and you may just be rewarded with new-found progress.


References

Clarkson PM, Hubal MJ. Exercise-induced muscle damage in humans. Am J Phys Med Rehabil. 2002; 81: S52-69.

Wang YX, Rudnicki MA. Satellite cells, the engines of muscle repair. Nat Rev Mol Cell Biol 2011; 13: 127-33.

Friday, 28 March 2014

MSc Mayhem and Dubious Data: an Ischaemic Pre-conditioning Pilot Study

Today's post will take a departure from previous ones and give you an insight into the kind of work that an MSc entails. Each year at the university I attend students are required to write-up a < 3,000 word report on a small, pilot-type trial conducted in the laboratory on their peers. I've had a very strong interest in ischaemic pre-conditioning and blood flow-restriction exercise for a number of years now, so I jumped on the opportunity to pursue this one... this was particularly timely given that my own Research Project will pursue one of over a hundred questions that I'm keen to answer related to ischaemic pre-conditioning.

Those of you familiar with the literature will notice that the methodology and research question do not add a novel contribution to the existing literature. Moreover, the numerous issues with such a small trial are a necessary part of the nature of the project. Therefore, this is not intended to be submitted to an academic journal for publication; instead, it sets the students up for their actual Research Projects that will commence after Easter and affords them an opportunity to hone their writing skills. As such, what follows in written in academese. Forgive me if you find it dry, although I must say that given how rarely I read blogs on the internet in comparison to journal articles, I often wish my fellow bloggers were a little more concise! 

With that out of the way, here's what we found from our little venture into the fascinating world of ischaemic pre-conditioning.

Abstract

Repeated series of ischaemia followed by reperfusion (ischaemic pre-conditioning (IPC)) mitigate cellular injury and may enhance exercise performance. Using a stratified-randomised, cross-over design, we compared incremental, maximal exercise performance on a cycle ergometer after IPC and control (CON) conditions in 1 female (age 24.5 years, mass 60 kg) and 4 males (age 23 ± 1 years, mass 76 ± 9 kg; mean ± SD). Tests were conducted in a counter-balanced order and performed at least 1-wk apart, at the same time of day. The IPC protocol entailed 3 series of 5-mins’ thigh ischaemia with 5-mins’ reperfusion between series, and the CON condition involved supine resting; cycling tests commenced 2 hours later. Resting blood lactate concentration (BLa) was measured; subsequently, BLa, heart rate (HR), oxygen consumption (V̇O2), power output, rating of perceived exertion, and respiratory exchange ratio were measured at the end of each exercise stage. IPC increased V̇O2peak from 51.2 ± 9.4 to 53.4 ± 10.3 ml.kg-1.min-1 (P = 0.04) without affecting other physiological variables or total exercise time (P > 0.05). IPC augments cycling V̇O2peak in moderately-trained young adults without affecting other measured physiological or performance variables; however, methodological issues with the present study warrant validation of these findings.

Keywords: exercise, lactate, oxygen uptake


Introduction

Ischaemic pre-conditioning (IPC) is characterised by brief, non-lethal, repeated ischaemic episodes followed by reperfusion of the target tissue. IPC subsequently exerts protective effects on organs such as the heart during prolonged, potentially injurious ischaemia (Murry, Jennings, & Reimer, 1986). IPC confers protection on multiple organs including skeletal muscle (Pang et al., 1995) and has recently been shown to improve maximal exercise performance (de Groot et al., 2010).

The triggers, sub-cellular mediators, and effector pathways underlying the effects of IPC exhibit intra- and inter-species differences that should be borne in mind when considering its mechanisms (Yellon & Downey, 2003). Myriad ligands have been shown to contribute to the protective effects of IPC on cardiomyocytes, including chemokines (Davidson et al., 2013), bradykinin and opioids (Hausenloy & Yellon, 2008); however, the factors underlying the beneficial effects of IPC on exercise performance are less well characterised.

Fatigue in exercise is associated with acute alterations in skeletal muscle including depletion of energy substrates like adenosine tri-phosphate (ATP) (Sahlin, Tonkonogi & Söderlund, 1998). The final common pathway in acute resistance to ischaemia-reperfusion injury is induction of intra-cellular kinases and subsequent modification of mitochondrial function (Das & Das, 2008). Murine evidence suggests that IPC thereby opens mitochondrial ATP-sensitive potassium channels, increasing ATP provision per mg of mitochondrial protein (Fryer et al., 2000), and IPC also induces closure of mitochondrial permeability transition pores by reducing oxidative stress (Halestrap, Clarke & Khaliulin, 2007).

Animal studies suggest that IPC augments muscle blood flow by increasing adenosine levels (Riksen, Smits & Rongen, 2004), nitric oxide availability (Kimura et al., 2007) and hypoxia-inducible factors (Dirnagl, Becker, & Meiser, 2009). Nitric oxide also thwarts mitochondrial oxygen consumption by maintaining an oxygen extraction reserve (Prime et al., 2009), and hypoxia-inducible factors may facilitate ATP generation by better matching oxygen supply to demand (O’Hagan et al., 2009). IPC is associated with increases in circulating growth factors and endothelial progenitor cells and hence improves endothelial function (Kimura et al., 2007). Furthermore, IPC may offset declines in endothelial function following exercise (Bailey et al., 2012a). Repeated application of IPC alone has recently been shown to induce favourable adaptations throughout the vascular tree both locally and systemically (Jones et al., 2014).

IPC may enhance blood lactate (BLa) clearance via up-regulation of intra- and extra-cellular lactate shuttles during exercise (Riksen, Smits & Rongen, 2004). IPC improves muscle contractility in animal models (Lawson & Downey, 1992), possibly by increasing efficiency of excitation–contraction coupling, reducing wasted ion pumping, and/or reducing anaerobic energy contribution (Pang et al., 1995); such changes could also mitigate BLa accumulation. Recent work has corroborated this in exercising humans by demonstrating that IPC may diminish BLa accumulation during an incremental running test in moderately-trained male runners (Bailey et al., 2012b). Importantly, this effect was independent of absolute exercise intensity.

Previously, IPC of the thighs was shown to improve maximal cycling performance by 1.6% and peak oxygen uptake (V̇O2peak) by 3% (de Groot et al., 2010); heart rate (HR), respiratory exchange ratio (RER) and V̇O2 did not differ between the IPC and sham-IPC steady-state, sub-maximal levels of the cycling test, however. In a subsequent study of less highly-trained cyclists, IPC enhanced total exercise time (TET) by ~4%, without affecting V̇O2peak (Crisafulli et al., 2011); moreover, IPC was associated with an increase in HRmax of ~3% (Crisafulli et al., 2011). These authors speculated that IPC may therefore also alter neural processes, perhaps influencing group III and group IV muscle afferents and thereby maintaining neural drive to the musculature.

The present study aimed to resolve these discrepant findings, and our primary aims were to determine whether IPC would increase V̇O2peak and prolong TET during an incremental cycling test to volitional exhaustion. The secondary aims were to examine the effects of IPC on BLa, HR and RER.

Methods

Participants

One female (age 24.5 years, mass 60 kg) and 4 males (age 23 ± 1 years, mass 76 ± 9 kg; mean ± SD) participated in the study, all of whom were non-smokers. Participants were heterogeneous with respect to their training statuses: one participant was not involved in systematic training whereas the others were. The procedures of the study were explained to the participants prior to their participation.

IPC

In a stratified-randomised, counter-balanced, cross-over study, participants visited the laboratory twice at the same time of day, with at least a week in between visits. Two and a half hours prior to exercise the participants began either: 1) three cycles of 5-mins’ unilateral tourniquet (D.E. Hokanson, Inc., Washington, USA) inflation around the proximal thigh to 200 mm Hg with 5-mins’ reperfusion between cycles during which the contralateral thigh underwent IPC; or 2) 30-mins’ rest to serve as the control (CON) condition. Five-min ischaemic episodes were chosen as this duration has been shown to be most protective against injury in a murine model of limb ischaemia (Bushell et al., 2002). Both conditions were performed in the supine position. Participants then returned to the laboratory two hours later to begin an incremental V̇O2peak test to volitional exhaustion on a cycle ergometer.

Exercise testing

Tests were held at the same time of day, used the same cycle ergometer wherever possible and were conducted under temperate environmental conditions (temperature 20.9 ± 0.6 °C, humidity 32 ± 3%, barometric pressure 748 ± 6 mmHg). Participants were instructed to abstain from alcohol, caffeine and strenuous physical exercise; they were also asked to replicate the same dietary intakes in the 24-hours prior to each test.

Each participant performed an incremental test on a cycle ergometer (Monark Exercise AB Ergomedic 874E, Vansbro, Sweden) at a fixed pedal cadence of 60 revs . min-1. Power output began at 60 W and was increased by 30 W every three-mins until volitional exhaustion.  Participants were verbally encouraged to exert maximum effort, and TET until exhaustion during each test was calculated.

Attainment of V̇O2peak was defined using the following criteria (Bird & Davison, 1997): 1) a plateau in the V̇O2 / exercise intensity relationship (an increase in oxygen uptake of < 2 ml . kg-1 . min-1 with an increase in exercise workload); 2) a final respiratory exchange ratio of ≥ 1.15; 3) a final HR within 10 beats . min-1 of the age-predicted maximum (220 beats . min-1 – age); 4) a post-exercise BLa of ≥ 8 mmol . L-1; 5) subjective fatigue and volitional exhaustion assessed via rating of perceived exertion (RPE) measurements using a scale from 6 to 20 (Borg, 1982).

Physiological measurements

Body mass and height were measured using an electronic scale (Adam CFW-150, Milton Keynes, UK) and stadiometer (seca, Hamburg, Germany), respectively. These were recorded immediately prior to each exercise test with participants wearing shorts, socks, T-shirts and underwear. During the exercise tests single capillary blood samples (25 µL) were taken from a finger tip immediately prior to exercise and during the final 15-s of each three-min stage for immediate determination of BLa using an automated BLa analyser (ARKRAY lactate Pro, Kyoto, Japan). RPE was recorded at the end of each three-min stage. Changes in BLa (mmol . L-1) were compared between conditions. The onset of BLa accumulation (OBLa) was selected as the time at which BLa first exceeded 4 mmol . L-1 (Jordan et al., 2010). OBLa values were calculated from second-order polynomial regression equations derived from individual participants’ BLa data plotted against power output. HR was recorded by a telemetry system (Polar Electro iS610, Oulu, Finland) during the last 30-s of each stage, and the mean and maximum values were recorded. Expired air samples were collected during the final min of each stage for determination of CO2 and O2 content (Servomex 1440 Gas Analyser, Brighton, UK) and volume (Harvard Dry Gas Meter, Massachusetts, USA) (Figure 1).



Figure 1. Study protocol. IPC, ischaemic pre-conditioning; L, left leg; R, right leg; BLa, blood sample for blood lactate concentration measurement; HR, heart rate measurement; RER, respiratory exchange ratio measurement; RPE, rating of perceived exertion measurement; V̇O2, oxygen uptake measurement. Filled boxes represent ischaemia; empty boxes represent reperfusion.  During cycling the boxes represent power output.

Statistics

Statistical analyses were performed using computer software (SPSS 17.0, Chicago, USA). Normality of data distribution was checked using Shapiro-Wilk’s test. Mean HRmax data for the IPC condition were not normally distributed, and after logarithmic-transformation the data were still not normally distributed; therefore, the non-parametric Wilcoxon signed ranks test was used to compare values. Student’s paired t-tests were used to compare differences in performance (TET) and physiological parameters (HRmax, OBLa, peak BLa, final RER, and V̇O2peak) between CON and IPC conditions during cycling. The 95% confidence intervals for the mean absolute pair-wise differences between conditions were calculated from the t-distributions and degrees of freedom. Absolute standardised effect sizes (ES) are provided to supplement the findings. In the absence of an appropriate anchor, an ES of <0 .2="" 0.2="" 0.6="" 1.2="" and="" considered="" large="" moderate="" small="" trivial="" was="">2.0 was considered very large (Hopkins, 2000). Descriptive data are presented as mean ± SD. Statistical significance was set at P ≤ 0.05.

Results

All participants completed the protocols. Mean HRmax, peak BLa, and RER during each cycling test were unaffected by IPC (Table I), although HRmax approached significance.

Table I. Mean (± SD) maximum heart rate (HRmax), peak blood lactate (Peak BLa), and respiratory exchange ratio (RER) during a cycling V̇O2peak test preceded by ischaemic pre-conditioning (IPC) or control (CON) conditions. CI, confidence interval.
Measure
CON
IPC
P-value
95% CI
Effect Size
HRmax (beats . min-1)
193 ± 11
181 ± 10
0.09
-26.6 to 3.0
1.04
Peak BLa (mmol . L-1)
10.7 ± 2.6
10.8 ± 1.9
0.97
-1.5 to 1.6
0.01
RER
1.10 ± 0.07
1.15 ± 0.04
0.25
-0.1 to 0.1
1.48

V̇O2peak was significantly higher in the IPC than the CON condition (Figure 2).


Figure 2. Individual (lines) and mean (squares) cycling V̇O2peak following control (CON) or ischaemic pre-conditioning (IPC) conditions. Error bars represent standard error. * P = 0.04; 95% confidence interval = 0.1 to 4.1 ml.kg-1.min-1, effect size = 0.22.

However, neither OBLa (Figure 3) nor TET (Figure 4) were different between CON and IPC conditions (P = 0.20 and P = 1.0, respectively).


Figure 3. Individual (lines) and mean (squares) cycling power at onset of blood lactate accumulation (OBLa) following control (CON) or ischaemic pre-conditioning (IPC) conditions. Error bars represent standard error. P = 0.20; 95% confidence interval = -12.9 to 45.7 W, effect size = 0.44.



Figure 4. Individual (lines) and mean (squares) cycling total exercise time (TET) following control (CON) or ischaemic pre-conditioning (IPC) conditions. Error bars represent standard error. P = 1.0; 95% confidence interval = -3.5 to 3.5 mins, effect size = 0.44.

Discussion

The major finding of the present study was that IPC increased cycling V̇O2peak by ~4% in healthy, moderately-trained young adults without affecting other physiological or performance variables. This suggests that the V̇O2 was higher at a given workload, indicating a reduced economy subsequent to IPC. The enhanced V̇O2peak is consistent with previous work by de Groot and colleagues (2010) who found an increase in of ~3% in well-trained cyclists in the absence of effects of IPC on sub-maximal physiological variables; however, in contrast to the present study, these authors reported an improved cycling performance after IPC. The present findings also conflict with those of another study of moderately-trained cyclists in which IPC enhanced TET by ~4%, without affecting V̇O2peak (Crisafulli et al., 2011).  Discrepancies between studies may have been due to differing training statuses of participants or protocol differences such as varying measurement durations.

It is difficult to reconcile our findings of an increased V̇O2peak without a concomitant increase in TET, and perhaps this is the product of methodological issues with the present study. Nonetheless, as cycling endurance performance is not determined exclusively by V̇O2peak (Coyle et al., 1988), IPC may have exerted effects on other aspects of physiology of relevance to cycling performance in the present study.  A time trial test may have been preferable to examine differences in performance between conditions as this would have been more externally valid. Furthermore, it is possible that participants’ pedalling cadences did not adhere to the target of 60 revs . min-1 in the V̇O2peak test used in the present study. Hence, perhaps differences between conditions in performance existed that were not detected through the measurement of TET alone.

de Groot and colleagues (2010) studied three females and 12 males and did not subsequently analyse their results for any possible inter-sex differences in responses to IPC; conversely, Crisafulli et al. (2011) analysed males alone. The present study included a mix of sexes, although it was under-powered to explore any inter-sex differences. Interestingly, previous work in murine models has demonstrated that the protective effects of IPC on heart tissue may be greater in females (Turcato et al., 2006); however, more recent evidence in humans has suggested that IPC may benefit recovery of various exercise performance indices in males more than females (Beaven et al., 2012), although this study was again limited by a small sample size. At present it remains to be definitively resolved whether inter-sex differences in response to IPC prior to exercise exist.

Our finding of no difference in HRmax is also at odds with previous work. Mean HRmax in the IPC condition was ~ 12 beats . min-1 lower than in the CON condition and this tended towards significance (P = 0.09). In contrast to this finding, IPC has previously been associated with increases in HRmax of ~3% (Crisafulli et al., 2011). This study used an impedance cardiograph to monitor haemodynamic parameters during exercise, which may have provided greater sensitivity to changes HR than the telemetry device in the present study.

BLa collection issues prevented the analysis of BLa accumulation in the present study. This would also have been facilitated by a more homogeneous sample, as this would have permitted the inclusion of a standardised, sub-maximal cycling test for determination of BLa accumulation; such a test would also be appropriate for determination of any IPC-induced differences in RPE. Typical resting values of BLa are 0.5 - 1.8 mmol . L-1, yet three participants exhibited values above this range prior to one of the exercise tests, and one participant had a perplexing value of 3.1 mmol . L-1 at rest. In another participant there was an anomalous decline in blood lactate as he neared exhaustion, and in three tests multiple sub-maximal lactate values were missing due to human error. These problems raised doubts over the validity of lactate measurements. As there were missing and peculiar data, the author opted to approximately determine OBLa and peak BLa alone.  Analysis of OBLa was selected rather than the BLa threshold using the Dmax method proposed by Cheng and colleagues (1992) as OBLa alone can be used to compare and predict endurance performance (Newell et al., 2007).

The finding of no effect of IPC on peak BLa is consistent with prior work on cyclists by de Groot and colleagues (2010) who also found no effects of IPC on peak BLa. These authors did not assess sub-maximal BLa, and IPC has since been shown to mitigate BLa accumulation and delay OBLa during a sub-maximal, incremental running exercise bout (Bailey et al., 2012b), without affecting peak BLa. Therefore, the possibility remains that IPC may alter BLa accumulation during sub-maximal cycling, although our findings suggest that IPC has no significant effects on OBLa. It should be noted, however, the point at which OBLa occurred could only be extrapolated from the available data, given that BLa was only sampled every three-mins. Perhaps differences would have been evident with more frequent and sensitive sampling procedures.

It is plausible that some participants did not reach a true V̇O2peak value; indeed, in both conditions one participant met just one of the criteria for the attainment of V̇O2peak. Furthermore, not one participant achieved a plateau in the oxygen uptake/exercise intensity relationship. Participants did not undergo familiarisation with the experimental protocol, and this may have helped ensure that V̇O2peak was attained. A shortcoming of the present study is that the participants’ physical activity levels were not standardised the day before the two exercise tests, and one participant had completed an exhaustive exercise bout the day prior to one of the tests which may have interfered with his test performance.

Methodological issues with the present study warrant further research to corroborate or refute our findings. No power calculation was made to determine an appropriate sample size, and a larger sample may have elucidated other significant effects of IPC. A more homogeneous sample with respect to sex and training status would have minimised the possibility of these variables confounding the results. Participants were privy to the study rationale and potential beneficial effects of IPC; therefore, the occurrence of placebo effects cannot be dismissed. Use of another arm with a sham-IPC protocol may have reduced the likelihood of this. Moreover, measures of reliability were not taken. Finally, it is possible that an alternative IPC protocol may have elicited superior results, and the study’s methodology precluded an understanding of the mechanisms underlying these results.

Future studies should be adequately powered and attempt to ascertain the mechanisms underlying the effects of IPC on performance and physiological variables in humans. A more externally valid exercise bout may be more suited to determining effects of IPC on performance. Whether IPC has different effects on the sexes should be explored, as should any influences of age and fitness. Application of IPC over the course of an exercise training programme could also be assessed following evidence that IPC may improve next-day recovery following strenuous exercise (Beaven et al., 2012) and repeated use may chronically enhance systemic endothelial function (Jones et al., 2014).

Conclusions

IPC increased cycling V̇O2peak by ~4% in healthy, moderately-trained young adults without affecting other physiological or performance variables, suggesting that IPC may acutely exert beneficial effects on certain physiological parameters of interest to athletes. Nonetheless, doubts concerning the validity of the data and the small sample size of the present study warrant further research to validate these findings.

Acknowledgements

The author would like to thank Dr Richard Ferguson and all of the Loughborough University Exercise Physiology MSc students for their efforts and time in supporting this project.


References

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