Changes in balance ability,power output,and stretch-shortening cycle utilisation after two high-intensity intermittent training protocols in endurance runners

Felipe Grcí-Pinillos*,Jun A.Párrg-MontillVíctor M.Soto-Hermoso, Pedro A.Ltorre-Román

aDepartment of Corporal Expression,University of Jaen,Jaen 23071,Spain

bDepartment of Sports Sciences,University of Granada,Granada 18071,Spain

Changes in balance ability,power output,and stretch-shortening cycle utilisation after two high-intensity intermittent training protocols in endurance runners

Felipe García-Pinillosa,*,Juan A.Párraga-Montillaa,Víctor M.Soto-Hermosob, Pedro A.Latorre-Romána

aDepartment of Corporal Expression,University of Jaen,Jaen 23071,Spain

bDepartment of Sports Sciences,University of Granada,Granada 18071,Spain

Purpose:This study aimed to describe the acute effects of 2 different high-intensity intermittent trainings(HIITs)on postural control,countermovement jump(CMJ),squat jump(SJ),and stretch-shortening cycle(SSC)utilisation,and to compare the changes induced by both protocols in those variables in endurance runners.

Long-distance runner;Postural control;Reactive strength;Training prescription;Vertical jump

1.Introduction

High-intensity intermittent training(HIIT)involves repeated short to long bouts of rather high-intensity exercise interspersed with recovery periods and has been used by athletes for almost a century now.1In fact,it is today considered one of the most effective forms of exercise for improving physical performance in athletes.1,2Traditionally,this type of training has been associated with sports modalities with high power requirements, although in recent years,a growing body of literature has focused on the benefit of fast intermittent exercises for endur-ance athletes.1–3This fact has enabled both endurance athletes and coaches to realise that both low-intensity training performed at high volumes and high-intensity training of short durations must be part of the training programs for endurance athletes,and previous papers have shown the effectiveness of training programs based on both methods.4,5

To date,most of research considering HIIT in endurance runners has been focused on the acute physiological and neuromuscular response.3,6–8However,surprisingly,little attention has been given to parameters such as balance ability and stretch-shortening cycle(SSC)utilisation,which have been associated with both athletic performance and injury risk.9–13Indeed,to the best of the researchers’knowledge,no previous study has focused on determining the effect of HIITs performed in a real situation—a fiel study—on postural control and SSCpreviously used in similar studies.17This device measures the contact time on the floo and the fligh time using photoelectric cells.Flight time was used to calculate the height of the rise using the body’s centre of gravity.Subjects performed 2 trials of every test,with a 15 s recovery period between them with the best trial being used for the statistical analysis.In all tests performed—CMJ,SJ—the pre-intermediate and pre-post differences(increase,Δ)were also calculated and used for the subsequent analysis.Participants were encouraged to achieve maximum performance throughout both running protocols.

Both CMJ and SJ tests are commonly used to discriminate between the effects of the SSC in various athletic populations.9,18Performance of the SSC is commonly measured using an added pre-stretch to a movement,such as comparing CMJ performance with SJ performance.9,18Researchers have measured SSC performance from CMJ and SJ jump heights as an augmentation of a prior stretch.19Pre-stretch augmentation (PSA)can be calculated asa percentage with PSA (%)=((CMJ-SJ)/SJ)×100.Another approach is to measure reactive strength(reactive strength index(RSI)calculated as CMJ–SJ height).20This is considered to be a measure of the ability to utilise the muscle pre-stretching during the CMJ.18,20Intermediate-pre and post-pre differences(Δ)were also calculated for PSA and RSI.

2.3.5.Postural control variables

A FreeMed©BASE model baropodometric platform was used for the stabilometric measurements(Sensormédica, Rome,Italy).The platform’s surface is 555×420 mm,with an active surface of 400×400 mm and 8 mm thickness manufactured by Sensormédica.The reliability of this baropodometric platform has been shown in previous studies.21Calculations of centre of pressure(CoP)movements were performed with the FreeStep©Standard 3.0 software(Sensormédica).A monopodal stabilometry test was performed before and immediately after (pre-and post-test,respectively)every training session (10×400 m and 40×100 m).Athletes stood on each of their lower limbs for 10 s(left leg first at the centre of the platform according to the manufacturer’s instructions and following the procedure of previous studies.22,23The following parameters were recorded for the left-and right-leg monopodal tests:length (Length)and area(Area)of the path described by the CoP and the speed for the CoP movement(Velocity).The average for both the left-and right-leg was calculated and used for the subsequent analysis.

2.4.Statistical analysis

Descriptive statistics are represented as mean±SD.Tests of normal distribution and homogeneity(Kolmogorov–Smirnov and Levene’s)were conducted on all data before analysis.A repeated measures analysis(ANOVA)(pre-,intermediate-,and post-test)was performed for CMJ,SJ,and SSC utilisation variables in both HIITs—10×400 m and 40×100 m—whilst a pre-post comparison was performed by Student’sttest in variables related to postural control.The level of significanc wasp＜0.05.Data analysis was performed using SPSS(Version 21; IBM,Armonk,NY,USA).

Table 1 HRR,RPE average running pace,and BLa accumulation during 2 highintensity intermittent trainings(mean±SD).

3.Results

HRR,RPE,average running pace,and BLa during both HIITs(10×400 mvs.40×100 m)are shown in Table 1. No significan differences were found between running protocols in the HRpeak,whilst the HRmeanwas significant y higher (p＜0.001)in the 40×100 m protocol.No significan differences between HIITs were found in either the ΔHRrecor the ΔHRR.Significan differences between both HIITs were found in the RPE(p=0.019),with lower values in the 40×100 m protocol.Running pace and%vVO2maxwere significant y (p＜0.001)faster during 40×100 m,and no significan changes were observed in pace throughout both running protocols.The speed maintained during each HIIT protocol is shown in Fig.1.No significan differences in 10×400 m or in 40×100 m were found.Finally,no significan differences were found in BLa.

Data from the ANOVA of CMJ,SJ,and SSC utilisation throughout both HIITs are reported in Table 2.No significan changes were found during the 40×100 m protocol,whilst significan improvements in CMJ and SJ(p=0.008 and 0.002, respectively)were found in the 10×400 m protocol.Indexes related to SSC utilisation(PSA and RSI)did not experience significan changes during any of the protocols.

A pre-post comparison regarding CoP movement(Area, Length,and Velocity)in monopodal support during both HIIT protocols is shown in Table 3.No significan changes were observed in the 40×100 m protocol,whilst significan impairments were observed in Area(p=0.006),Length(p=0.001), and Velocity(p=0.004)during the 10×400 m protocol.

4.Discussion

The main purpose of this study was to describe the acute effects of 2 different HIITs on postural control,CMJ,SJ,and SSC utilisation in endurance runners,as well as determining whether a protocol with a higher number of shorter runsdegree of anaerobic glycolysis activation(BLa),24as well as the capability of the leg extensor muscles to generate mechanical power(CMJ and SJ).25This study showed that in spite of the high level of fatigue reached—as demonstrated by cardiovascular response,BLa and RPE—the vertical jump ability was not impaired after HIITs in endurance runners.In the 40×100 m protocol the CMJ and SJ performance remained unchanged—there were no significan differences according to baseline values.Even more surprising was that the best values for CMJ and SJ performance for the 10×400 m protocol were obtained post-test.It might be expected that power performance after running exercises inducing high levels of fatigue would decreased.Nevertheless,some previous studies6,7,26,27found post-activation potentiation(PAP)—a significan improvement in muscular power as a result of previous muscular work28,29—after running exercises in endurance runners.These data show that,despite high levels of fatigue,trained subjects can maintain their strength and power levels,and therefore their work capacity in terms of running pace,during HIIT protocols performed abovevVO2max.Since fatigue level after both workouts was similar and pace was maintained over both HIITs, neither level of fatigue reached nor pacing strategy for each HIIT seems to be responsible for changes induced in jumping ability.The authors suggest that the running pace might be responsible for these muscle power output changes.A faster running pace during the 40×100 m protocol(faster average pace and higher%vVO2max)will recruit additional fast twitch motor units for relatively short durations.30

Data obtained from SSC utilisation support and reinforce that statement.It might be expected that SSC utilisation,indirectly measured by means of PSA and RSI,would decrease throughout both HIITs.Despite a trend towards lower SSC utilisation being observed in both HIITs,no significan changes were found in PSA or RSI during either running protocols.As far as the authors know,the information available about SSC utilisation in endurance athletes is limited18,31,32and no previous studies have analysed the fatigue-induced changes in SSC utilisation during running exercises so the comparison with previous studies is quite difficult Padua et al.33concluded that some parameters associated with SSC utilisation were unaffected after fatigue,the opposite results found by Moritani et al.34

Basic muscle function is define as the SSC,where the pre-activated muscle is firs stretched(eccentric action)and then followed by the shortening(concentric)action.35However, neuromuscular fatigue has traditionally been examined using isolated forms of isometric,concentric or eccentric actions, whereas none of these actions are naturally occurring in human ground locomotion.Parameters related to SSC utilisation,such as PSA or RSI,have been used for monitoring training adaptations over a sport season18and have been associated with performance enhancement,injury prevention and fatigue mechanisms.12,33,36Based on the results obtained,the authors suggest that monitoring parameters such as RSI and PSA during running exercises might provide interesting information about acute responses to training sessions and about training adaptation throughout the season.

Postural control is a complex function that involves keeping the vertical projection of the centre of gravity within the base of support.11As indicated by Degache et al.37postural control is a permanent re-establishment process of balance,which depends on the orientation information derived from 3 independent sensory sources:somatosensory,vestibular,and visual inputs. Balance is actively controlled by the central nervous system, which calls into action various relevant postural muscles when they are required;38therefore,postural control is also dependent upon refl xive and voluntary muscle responses.39On the other hand,fatigue following physical exercise is caused by a combination of physiological processes,occurring at both central and peripheral levels,which mainly deal with the inability to produce an expected force or with the increase in the onset delay of movement.30It has been shown that exercises such as running,cycling,cycle ergometer,walking,ironman triathlon, or mountain ultra-marathon affect postural control.22,37–39This type of exercise involving the whole organism deteriorates the sensory proprioceptive and exteroceptive information and/or their integration,and/or decreases the muscular system efficien y.38It is therefore well documented that muscular exercise is a cause of aggravation of postural sway since the increase of energy needs amplifie liquid movements and cardiac and respiratory muscular contractions.40In addition,when muscular exercise generates fatigue,it affects the regulating system of postural control by its effects on the quality and treatment of sensory information,as well as motor command.Indeed,muscular exercise induces perturbations of the neuromuscular system that involve changes in muscle strength7and postural control.22

As for balance ability and fatigue-induced changes by 2 different HIITs in endurance runners,the data obtained in this study are partially consistent with previous works showing that CoP movements in monopodal support were greater—worse balance ability—after 2 different HIITs(10×400 m: 18.33%–40.83%,40×100 m:8.24%–12.86%)according to pre-test or baseline values.Nevertheless,despite no differences being found between fatigue levels induced by either HIIT protocols,reductions only were statistically significan after the 10×400 m protocol,whilst no significan reductions were seen in the 40×100 m protocol.To date,previous papers focused on checking the fatigue-induced changes after running exercises in balance ability reported impairment.22,37,40However,as indicated by Degache et al.,37the conditions under which the different exercises are performed influenc postural control in different ways.As mentioned earlier,neither level of fatigue reached nor pacing strategy for each HIIT seems to be responsible for changes induced in balance ability.However,this study seems to indicate that short runs performed at high intensities (40×100 m)cause smaller impairments in postural control than longer runs performed at a slower pace(10×400 m). Anyway,more research is needed to highlight the physiological basis of that assumption.

Finally,the main limitation of this study was not to include more indications on a precise intensity to maintain.Despite thatvVO2maxwas reported,coaches usually prescribe in terms of %HRmaxor best performance on a distance.Notwithstandingtraining with unstable platform on athletes’stabilometry.J Strength Cond Res2013;27:2189–97.

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Received 6 March 2015;revised 28 April 2015;accepted 22 May 2015

Available online 15 September 2015

Peer review under responsibility of Shanghai University of Sport.

*Corresponding author.

E-mail address:fegarpi@gmail.com(F.García-Pinillos).

http://dx.doi.org/10.1016/j.jshs.2015.09.003

2095-2546/©2016 Production and hosting by Elsevier B.V.on behalf of Shanghai University of Sport.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Methods:Eighteen recreationally trained endurance runners participated in this study and were tested on 2 occasions:10 runs of 400 m with 90 s recovery between running bouts(10×400 m),and 40 runs of 100 m with 30 s recovery between runs(40×100 m).Heart rate was monitored during both HIITs;blood lactate accumulation and rate of perceived exertion were recorded after both protocols.Vertical jump ability(CMJ and SJ)and SSC together with postural control were also controlled during both HIITs.

Results:Repeated measures analysis revealed a significan improvement in CMJ and SJ during 10×400 m(p＜0.05),whilst no significan changes were observed during40×100 m.Indexes related to SSC did not experience significan changes during any of the protocols.As for postural control,no significan changes were observed in the 40×100 m protocol,whilst significan impairments were observed during the 10×400 mprotocol(p＜0.05).Conclusion:A protocol with a higher number of shorter runs(40×100 m)induced different changes in those neuromuscular parameters than those with fewer and longer runs(10×400 m).Whereas the 40×100 m protocol did not cause any significan changes in vertical jump ability, postural control or SSC utilisation,the 10×400 m protocol impaired postural control and caused improvements in vertical jumping tests.

©2016 Production and hosting by Elsevier B.V.on behalf of Shanghai University of Sport.This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).