Effects of small-volume soccer and vibration training on body composition,aerobic fi tness,and muscular PCr kinetics for inactive women aged 20—45

Luke J.Connolly,Suznne Scott,Mni Mohr,b,c,Gioros Erm idis,d,Ross Julin,e, Jens Bnsbo,Srh R.Jckmn,Jonn L.Bow tell,Rosemry C.Dvies,Susn J.Hopkins, Richrd Seymour,Kren M.Knpp,Peter Krustrup,,Jonthn Fulord

aSport and Health Sciences,College of Life and Environmental Sciences,St Luke’s Campus,University of Exeter,Exeter EX1 2LU,UK

bFaculty of Natural and Health Sciences,University of the Faroe Islands,Torshavn 100,Faroe Islands

cDepartment of Food and Nutrition,and Sport Science,University of Gothenburg,Gothenburg 40530,Sweden

dDepartment of Physical Education and Sport Science,Democritus University of Thrace,Komotini 69100,Greece

eInstitute of Sports and Preventive Medicine,University of Saarland,Saarbru¨cken 66123,Germany

fCopenhagen Centre for Team Sport and Health,Department of Nutrition,Exercise and Sports,University of Copenhagen,Copenhagen 2200,Denmark

gCollege of Engineering,Mathematics and Physical Sciences,University of Exeter,Exeter EX4 4QF,UK

hNIHR Exeter Clinical Research Facility,University of Exeter Medical School,Exeter EX2 5DW,UK

Effects of small-volume soccer and vibration training on body composition,aerobic fi tness,and muscular PCr kinetics for inactive women aged 20—45

Luke J.Connollya,Suzanne Scotta,Magni Mohra,b,c,Giorgos Erm idisa,d,Ross Juliana,e, Jens Bangsbof,Sarah R.Jackmana,Joanna L.Bow tella,Rosemary C.Daviesa,Susan J.Hopkinsg, Richard Seymourg,Karen M.Knappg,Peter Krustrupa,f,Jonathan Fulfordh,*

aSport and Health Sciences,College of Life and Environmental Sciences,St Luke’s Campus,University of Exeter,Exeter EX1 2LU,UK

bFaculty of Natural and Health Sciences,University of the Faroe Islands,Torshavn 100,Faroe Islands

cDepartment of Food and Nutrition,and Sport Science,University of Gothenburg,Gothenburg 40530,Sweden

dDepartment of Physical Education and Sport Science,Democritus University of Thrace,Komotini 69100,Greece

eInstitute of Sports and Preventive Medicine,University of Saarland,Saarbru¨cken 66123,Germany

fCopenhagen Centre for Team Sport and Health,Department of Nutrition,Exercise and Sports,University of Copenhagen,Copenhagen 2200,Denmark

gCollege of Engineering,Mathematics and Physical Sciences,University of Exeter,Exeter EX4 4QF,UK

hNIHR Exeter Clinical Research Facility,University of Exeter Medical School,Exeter EX2 5DW,UK

Purpose:The present study investigated the effects of 16 weeks of small-volume,small-sided soccer training soccer group(SG,n=13)and oscillating whole-body vibration training vibration group(VG,n=17)on body composition,aerobic fi tness,and muscle PCr kinetics in healthy inactive premenopausal women in comparison w ith an inactive control group(CO,n=14).

Methods:Training for SG and VG consisted of tw ice-weekly 15-m in sessions w ith average heart rates(HRs)of～155 and 90 bpm respectively. Pre-and post-measurements of body composition(DXA),phosphocreatine(PCr)on-and off-kinetics,and HR measurements during standardised submaximal exercise were performed.

Results:A fter 16 weeks of training in SG,fatpercentage was lowered(p=0.03)by 1.7%±2.4%from 37.5%±6.9%to 35.8%±6.2%and the PCr decrease in the quadriceps during knee-extension ramp exercise was attenuated(4%±8%,p=0.04),w ith no changes in VG or CO(timegroup effect:p=0.03 and p=0.03).Submaximal exercise HR was also reduced in SG after 16 weeks of training(6%±5%of HRmax, p=0.01).

Conclusion:Shortduration soccer training for16 weeks appears to be sufficient to induce favourable changes in body composition and indicators of aerobic fi tness and muscle oxidative capacity in untrained premenopausal women.

CopyrightⒸ2014,Shanghai University of Sport.Production and hosting by Elsevier B.V.A ll rights reserved.

Fat percentage;Heart rate;MRS;PCr kinetics;Small-sided soccer

1.Introduction

It is well documented that physical activity(PA)can improve the cardiorespiratory fi tness and health profi le and may lower the risk for several cardiovascular and metabolic diseases.1However,inactive behavior has continued toincrease over the past few decades,2,3w ith lack of time commonly cited as an issue preventing women from meeting PA recommendations.4Focus should therefore be placed on developing PA interventions for inactive women for which high compliance rates can be achieved while obtaining the positive health benefi ts of exercising.

As soccer is one of the most popular sports in the world, w ith over 29 m illion registered women players globally,5it may serve as an appealing,inexpensive PA for inactive women.Soccer is a motivational and social activity6,7and, most importantly,participation in small-sided recreational soccer games has been shown to be an effective healthpromoting activity for both untrained men8—11and women.12—18In untrained premenopausal women,Krustrup etal.17and Andersen etal.18found thatparticipating in tw ice-weekly 1-h sessions of small-sided recreational soccer or outdoor continuous running for 16 weeks produced a number of positive health benefi ts.Maximal oxygen uptake,lean mass,and heart function were increased and fat mass and systolic blood pressure(BP)were reduced for both groups.In addition,a decrease in diastolic BP and low-density/high density lipoprotein cholesterol ratio was evident for the soccergroup only, and the cardiac adaptations induced by the training were considered to be more consistent when compared to continuous running.18Similar health benefi ts have been observed after 12 weeks of soccer,2—3×1 h per week,organised as a workplace intervention outside working hours.14Although these interventions produced positive health benefi ts,they required participants to exercise for 1 h per session,a length of time not necessarily easy to accommodate w ithin peoples’daily routine.However,it is not known whether the same health benefi ts can be achieved w ith a reduction in training session duration.

Whole-body vibration(WBV)training is an alternative exercise modality that is becom ing increasingly popular in gyms and may address time constraints and compliance issues in inactive populations19due to the shortduration of sessions. However,rather than a cardiovascular focus,much of the research w ithin this area has exam ined muscle strength20and power,21,22postural control in the elderly23and bone m ineral density in postmenopausalwomen.24Acute responses to WBV training(vertical and oscillating),in combination w ith upperand lower-body exercises,have shown thatoxygen consumption increases linearly as load,frequency(f),and amplitude (A)rise.25,26However,only a small number of studies have exam ined the effects of WBV training as an intervention to improve the cardiovascular risk profi le in inactive populations. Song et al.27revealed a significant decrease in weight,waist circum ference and BM I after 8 weeks of oscillating WBV training,10 m in tw ice a week,in obese postmenopausal women,although this was not accompanied by changes in body fatpercentage.Likew ise,18 months of WBV training in postmenopausal women performed tw ice a week(60 min/ session)was associated w ith reductions in body fatpercentage and abdominal fatmass and an increase in lean body mass.28However,these changes were not significantly different from other training modes(e.g.,aerobic dance).Thus,to date it is unclear whether oscillating WBV training provides sufficient cardiovascular stimulation to improve the health profi le of inactive premenopausal women after a short intervention period.

As such we aimed to investigate some of the potential differences in health benefi ts thatmay arise between two very different exercise modalities,thereby possibly inform ing the decision process of individuals when selecting an exercise regime to fi t into the limited time available to them.Hence,the goal of the present study was to undertake a pilot study to examine the feasibility of measuring cardiovascular and metabolic adaptations in inactive m iddle-aged premenopausal women in response to participation in 16 weeks of small-sided soccer training and WBV training.The main focus was to assess whether measureable changes could still be detected w ith short exercise durations,when exam ining sim ilar group sizes to those that have shown beneficial health effects w ith longer duration exercise intervention9—11,16and to assess the differences in responses between exercise modalities.We hypothesised that low-volume small-sided soccer training would reduce fatmass,resting heart rate(HR)and HR during submaximal tasks,and would improve muscle PCr kinetics.In contrast,it was hypothesised that WBV training would not provide a sufficient cardiovascular and metabolic challenge to induce equivalentadaptations.

2.M ethods

2.1.Participants

Participants were recruited through advertisements in the local newspaper,community venues,and local radio stations. No financialorother inducements were offered to participants. Allparticipants completed a questionnaire prior to the training intervention to confi rm that they were premenopausal and that none of them were smokers,pregnant,or on medication. Participants also confi rmed there were no known medical conditions that would exclude them from undertaking in an exercise program.None of the participants had been taking part in regular PA forat least2 years.This was established via questionnaire at baseline requiring participants to detail time spent weekly undertaking activities likely to cause significant increases in cardiovascular output.Activities listed included jogging,cycling,sw imm ing,gym sessions,fi tness classes,and sporting events.In addition,the participants had no previous experience of participating in competitive orprofessional level sportand had little or no experience of playing soccer or using WBV equipment.A lthough not directly monitored,the participants were encouraged not to change their dietary intake for the duration of the study and,apart from the intervention, were requested to maintain their normal lifestyle.All the participants gave their w ritten informed consent after they were fully informed of the potential benefi ts,possible risks, and discom forts associated w ith the study.The study was approved by the National Research Ethics Service(NRES) (12/SW/0045)and the institutional research ethics comm ittee (NHS 2012/329).

The participants were random ly assigned to a soccer group (SG,n=21),a WBV group(VG,n=21),or a controlgroup who performed no physical training(CO,n=24).Sw itching between groups was generally not possible.However,two participants who had initially been assigned to SG were reassigned to VG prior to any training sessions taking place,as itwas impossible for them to attend any of the soccer training sessions due to work comm itments at those times.Eight,four, and 10 participants in SG,VG,and CG,respectively w ithdrew from the study due to pregnancy,personal problems,minor injuries,or low compliance w ith the training.

2.2.Study design

Of the 44 participants of Caucasian(n=42)and Southeast Asian(n=2)origin who completed the study;i.e.,SG (n=13),VG(n=17),and CO(n=14),those in SG and VG trained for 16 weeks,while CO continued their normal daily lives.The participants were assessed before and after the intervention period w ith continuous recordings of HR throughout the training sessions.

2.3.Training intervention

The soccer training was organised as small-sided games made up of two teams w ith no goalkeepers and the aim of the game was to score in the opposition’s goal.The sessions took place tw ice a week for 13.5 min on various playing surfaces, including outdoor natural grass,artificial turf and,during bad weather,an indoor court.Allsurfaces were 15—25 m w ide and 20—40 m long.Each participant was supplied w ith relevant soccer footwear for indoor and outdoor facilities.Three to four morning and evening training sessions were organised every week in order to ensure thateach participantcould attend two of them,w ith a recommended gap ofat least48 h between sessions and a m inimum gap of at least24 h between sessions.A ll sessions were fully supervised by an instructor who had previous experience of playing soccer and could actas an extra participantwhen teams were unequal.Due to the variation in session participants,the small-sided gameswere played as2 v 2,3 v 3 or 4 v 4.Each training session was preceded by a standardised 2-m in warm-up consisting of the fi rst six 20-m shuttle runs of the Yo-Yo interm ittentendurance level1 test(YYIE1).29After each 40-m run,the participantshad a 5-sactive recovery period during which they walked 2×2.5 m.

The 13.5-m in WBV training was also adm inistered tw ice a week on a WBV plate(Galileo Sport,Novotec Medical GmbH,Pforzheim,Germany)w ith at leasta 24-h gap between sessions.The participants were instructed to remove their shoes,stand on the plate w ith slightly bent knees and heels touching the board and bring their weight over the forefoot. The protocol consisted of a 3-m in warm-up at a frequency of 6 Hz w ith amplitude of 2 mm.A fter the warm-up,the participants completed 1-m in bouts of1)static squats(at30°knee flexion),2)dynam ic squats(between 30°and 90°knee flexion),3)pelvic floor muscle loading,4)alternating“hump back,swallow back”,5)static squats(at 30°knee flexion),6) dynam ic squats(between 30°and 90°knee flexion),and 7) pelvic floor muscle loading.Each 1-m in boutwas followed by 1 m in of recovery.For the duration of the study,the fi rst four exercises were completed ata frequency of 12 Hz.For the fi rst 4 weeks,the final three exercises were also completed at12 Hz and increased to 18 Hz for weeks 5—7 and 27 Hz for the remaining 9 weeks.Vibrational amplitude increased from 1 mm in the fi rst week to 1.5 mm in weeks 2—3,2 mm in weeks 4—5,2.5 mm in week 6,3 mm in weeks 7—9,3.5 mm in week 10,and 4 mm in weeks 11—16.A load of 4,6,and 8 kg was also applied in weeks 14,15,and 16 for exercises 1, 2,5,and 6.AllWBV sessions were organised on a one-to-one basis w ith a trained supervisor to ensure safety and guidance in the required exercises.

Compliance for both training groups was monitored,w ith attendance records controlled by the supervisors.

2.4.Pre-and post-exercise intervention testing procedures

The subjects were fam iliarised w ith all testing procedures on at least one occasion before baseline testing and no PA was performed 2 days prior to testing.A ll measures were performed at baseline and were subsequently repeated w ithin 1 week of the completion of the 16-week training intervention.

Height(Seca stadiometer SEC-225;Seca,Hamburg,Germany),resting HR and BP were obtained after at least 10 m in of restwith the participant in a seated position.A minimum of five measurements were performed using an automatic upperarm BP monitor(M 7;OMRON,Lake Forest,IL,USA)w ith an average value calculated.

In order to exam ine body composition,a total body DXA scan was performed(GE Lunar Prodigy,GE Healthcare, Bedford,UK),and fatand lean tissue were compartmentalised using standard regions of interest.

To exam ine muscle phosphorus metabolite concentrations at rest and during two different exercise protocols,the participants were positioned in the bore of a 1.5 T superconducting magnet (Intera; Philips, Amsterdam, the Netherlands)at the University of Exeter Magnetic Resonance Research Centre.Prior to the exercise bouts,baseline measurements were taken.On completion,two different exercise regimes were carried out to exam ine different facets of muscle function.In the fi rst,PCr recovery kinetics was exam ined by undertaking shortbouts of continuous exercise.Subsequently, after a recovery period,a ramp exercise protocol was undertaken in which the workload was continually increased until the point of participant failure.

The participants were positioned in the scanner head fi rst in a prone position such that the subject’s right quadriceps muscle was centred directly over a 6-cm31P transm it/receive surface coil.They were subsequently secured to the scanner bed using Velcro straps at the thigh,buttocks,lower back,and m iddle back to minim ise extraneous movement.In order to undertake exercise testing,a custom-designed nylon ergometer frame fi tted onto the bed in alignment w ith the subject’s feet and a base unit was positioned behind the bed.Cuffs w ithVelcro straps were secured to the subject’s footand attached to a rope which passed around pulleys housed w ithin the frame to the base unit,where they were attached to non-magnetic weights.

Prior to the beginning of exercise,images were acquired to confi rm that the quadriceps muscle was positioned directly above the31P coil.Subsequently,a pre-exercise baseline spectrum was acquired w ith long repetition time(TR=20 s) in which the relative unsaturated peak amplitudes could be determined.Molar concentrations of PCr and ATP were subsequently calculated via the ratio of Pi:PCr and Pi:ATP, assum ing a resting concentration of ATP of 8.2 mmol/L.

The exercise protocol consisted of one-legged knee extensions,which resulted in the lifting of weights via the pulley system.The extensions took place at a frequency of 0.67 Hz w ith the foot moving over a distance of～0.22 m, w ith both visualand audio cues being given to ensure that the rate of contraction was maintained at the desired value.To exam ine PCr recovery kinetics,two 24-s bouts of exercise were performed,separated by a recovery period of 4 m in.In order to obtain a significant PCr depletion(～40%),thereby maxim ising the accuracy of the recovery data fi tting,exercise was undertaken w ith weights of mass 1 kg less than the maximum weight each subject achieved during the previous fam iliarity session.As the rate of PCr recovery has previously been shown to be pH dependent,30,31exercise bouts were lim ited to 24 s as we have previously determ ined that exercise for that period does not lead to a measurable decrease in pH.The ramp protocol involved the participants continually exercising to volitional fatigue.Initially,exercise was carried out w ith a weight of 1 kg mass.This was then increased by 0.5 kg every 30 s until exhaustion,the time of which was recorded.During exercise and recovery,31P data were acquired every 1.5 s and phase cycling w ith four phase cycles was employed,leading to spectra being acquired every 6.0 s.

2.5.Measurements during training

HR was recorded during WBV training for 10 participants, using Polar T34 belts(Polar Electro Oy,Kempele,Finland) and noted each m inute during the 13.5-m in protocol.The remaining seven participants in VG opted not to have HR recorded during WBV training.HR was recorded during soccer warm-ups and training sessions using Polar T34 belts and a portable 15-Hz global positioning system(GPS;SPIPro X,GPSports,Canberra,Australia).Data were subsequently downloaded using Team AMS v.1.5(GPSports)where average and peak HR was automatically generated following a userdefined time split for the session duration.Individual HRpeakwas determ ined as the highest HR reached w ithin a single soccer session across the length of the study.HR was also analysed for the last 15 s of each YYIE1 warm-up to determ ine any change in HR over time for the same given work rate.Using GPS measurements,only those who covered a distance of≥150 m for the YYIE1 in the given time were included in the analyses.

2.6.Data analysis

The acquired spectra were quantified via peak fi tting, assum ing prior know ledge,using the jMRUI(version 3) software package employing the AMARES fi tting algorithm.32Spectra were fi tted assum ing the presence of the follow ing peaks:Pi,phosphodiester,PCr,α-ATP(2 peaks,amplitude ratio 1:1),γ-ATP(2 peaks,amplitude ratio 1:1),andβ-ATP(3 peaks,amplitude ratio 1:2:1).Intracellular pH was calculated using the chem ical shiftof the Pispectral peak relative to the PCr peak.33

For the PCr values follow ing the 24-s exercise period,PCr recovery was fi tted w ith Prism 5 software(GraphPad Software Inc.,La Jolla,CA,USA)by a single exponential of the form:

where PCrendis the value at the end of exercise,PCr(0)is the difference between the PCr at end exercise and fully recovered,tis the time from exercise cessation andτis the time constant for the exponential recovery of PCr.Each 24-s recovery period was fi tted individually and the time constants determ ined for each before being averaged to give the value quoted for the trial.

For the ramp protocol,for each participant the PCr depletion at the end of exercise was determ ined.In addition,the PCr depletion at the same time point from both visits was determined,with the time selected corresponding to the shorter exercise finish time from the two visits.

2.7.Statistics

Statistical analyses were performed using the Statistical Package for the Social Sciences(SPSS,v.20,SPSS Inc., Chicago,IL,USA).Before analysis,data were checked for normality using a Shapiro—W ilk test.Non-normally distributed data were assessed using the Kruskal—Wallis test.Homogeneity of variance was determ ined using Levene’sF-test. Repeated measures analysis of variance(ANOVA)were used to evaluate data for 0,8(YYIE1 warm-up only),and 16 weeks of the intervention w ith group as between-subjects factor and time as the repeated factor.Effect sizes(partialη2)were also reported for interpretative purposes w ith 0.01,0.06,and 0.14 regarded as a small,moderate,and large effect.34Due to the mean age(40±5 years)and age range(29—46 years)of the participants,repeated measures analysis of covariance (ANCOVA)w ith age as a covariate were also used.However, as the covariate did not have a significant(p＞ 0.05)relationship to any of the outcome variables,only ANOVA data are reported.When a significantF-value was detected,data were subsequently analysed usingpost hoc ttests w ith a Bonferroni correction.Between-group differences in baseline characteristics as well as intervention-induced changes were evaluated by a one-way ANOVA.Significance was selected at the levelofp＜0.05.Allstatisticalanalyses were presented as mean±SD unless otherw ise stated.

Table 1 Baseline characteristics and(absolute change)in fat mass and lean mass follow ing 16 weeks of training for the soccer(SG),vibration(VG),and control(CO) group(mean±SD).

3.Results

For the participants who completed the study(SG,n=13; VG,n=17;CO,n=14),no group differences were present for the pre-intervention baseline values(Table 1).

3.1.Fat mass and lean body mass

Fig.1.Fat percentage for inactive premenopausal women after 16 weeks of soccer training(SG),whole-body vibration training(VG),or continuation of a sedentary lifestyle(CO)(mean±SD).*Significant difference from baseline.#Significant delta value difference from VG follow ing 16 weeks of training.

A significant group×time interaction was found for total fatpercentage(p=0.03;partialη2=0.15).Posthocanalysis revealed that in SG,fat percentage significantly decreased by 1.69%±2.38%(p=0.03)during the 16-week intervention period,w ith no changes for VG or CO(Fig.1).A significant group×time interaction was also evident for fat mass of the trunk(p=0.03;partialη2=0.16)and android(p=0.04; partialη2=0.15).Posthocanalysis revealed that fatmass of the trunk and android(central fat predictive of body shape) significantly decreased by 1.02± 1.40 kg(p=0.02)and 0.17±0.27 kg(p=0.04)respectively in SG over16 weeks of training,w ith no changes for VG or CO(Table 1).The changes in fatpercentage(p=0.03)for SG was significantly greater than for VG,as was the changes in fat mass of the trunk(p=0.03)and android(p=0.03).Lean mass was not significantly altered in any of the three groups follow ing the 16-week intervention(Table 1).

3.2.Magnetic resonance spectroscopy measurements

During one-legged knee-extensor ramp exercise,a significant group×time interaction was evident(p=0.03;partial η2=0.18)for PCr depletion at the same time for the pre-and post-tests.In SG,after 16 weeks of training the degree of PCr depletion was less(p=0.04)(PCr content relative to baseline:54.7% ±12.5%vs.59.1% ±12.6%for pre-vs.posttraining)w ith no change for VG or CO(Table 2).Data for a representative participant is illustrated in Fig.2.At the same time-point a significant main effect w ith time was seen for muscle pH but no significant interaction effects w ith group (SG:6.95± 0.09vs.6.98± 0.07;VG:6.95± 0.05vs.6.98±0.06).Follow ing 16 weeks of training,the rate of PCr recovery was not significantly altered after bouts of 24 s constant load exercise(SG;τ:35.1±8.7vs.30.7±7.7 s;VG; τ:32.8± 9.3vs.34.6± 9.6 s;CO;τ:35.5± 8.8vs.32.7±5.9 s,for pre-vs.post-training,respectively)in any of the groups.

Table 2 Summary of magnetic resonance spectroscopy measurements prior to and at the end of the ramp exercise testperformed before and after the 16-week intervention period in the soccer group(SG),the vibration training group(VG),and the inactive control group(CO)(mean±SD).

3.3.HR and BP

A fter 16 weeks,resting HR was notsignificantly lowered in SG(77±8vs.73±8 bpm),VG(74±11vs.72±11 bpm), or CO(77±9vs.74±6 bpm),respectively.Resting systolic and diastolic BP was also unaltered in allgroups follow ing the 16-week intervention(SG:117±15/75±11vs.119±13/ 76± 10 mmHg;VG:121± 13/78± 9vs.118± 17/ 77± 11 mmHg;CO:112±16/74±11vs.113± 17/ 74±10 mmHg,respectively).

The average HR during WBV training conducted in the fi rst and last week of training were 92±14 and 92±17 bpm, respectively.The average and peak HR during the soccer training(n=13)was 159±8 and 178±6 bpm and 155±7 and 175±6 bpm during the fi rst and last week of training, respectively,which corresponded to 85% ± 5% and 96%±4%,and 83%±3%and 93%±2%,respectively,of peak HR(HRpeak).

3.4.Physiological response to the submaximalYYIE1 test

There was a significant time effecton HR(p＜0.01;partial η2=0.54)during the last15 s of the YYIE1 warm-up for SG. HR during the last15 s of the YYIE1 warm-up was 160±7, 157±6,and 148±9 bpm after 0,8,and 16 weeks of the study respectively,corresponding to 85%±6%,84%±5%, and 79%±5%of HRmax.A significantdecrease of 6%±5% and 5%±5%of HRmaxwas evident when comparing 0—16 weeks(p=0.01)and 8—16 weeks(p=0.04),respectively.

Fig.2.PCr depletion during a ramp exercise test,pre-and post-the 16-week soccer training intervention for a representative participant.

4.Discussion

The main findings of the present study were that smallvolume recreational soccer training resulted in several benefi ts in body composition and aerobic fi tness of inactive premenopausal women relative to either WBV or control participants.Specifically,fat percentage decreased along w ith reductions in HR during a submaximal running task and positive adaptations in muscle oxidative capacity,as determined by measurements of PCr kinetics.

4.1.Energy expenditure and fat mass

The mean HR for the SG during training sessions was 155 bpm,corresponding to～85%of HRmax,which is markedly higher than the 90 bpm observed for the WBV training group.The HR during the soccer training was found to be sim ilar to values for 1-h small-sided training sessions for untrained premenopausal females35and slightly higher than that observed in untrained and habitually active 25—65-year-old female hospital employees.14The high HRs in the soccer group during training illustrates the energy demanding nature of small-sided games,w ith multiple intense actions such as accelerations,decelerations,rapid changes of direction,and unorthodox movements having been observed to occur as often as every～4 s on average.12,13,35

A significant finding of the present study is that the fat percentage was reduced markedly(1.7%)in the SG over the 16-week intervention despite the short duration of the tw iceweekly training sessions,whereas no changes were observed for the VG and the CO.The decrease in fat percentage was very consistent for the SG participants w ith as many as 92%of them having a lowered fat percentage after 16 weeks,i.e.,all exceptone,whereas this was only the case for 41%of the VG participants and 43%of the control subjects.Interestingly,the decrease in fatmass for the SG was 1.4 kg which is sim ilar to values reported in previous studies with 12—16 weeks of 1-h tw ice-weekly recreational soccer training for untrainedwomen13—17even though the training volume was only a quarter of that in the other studies(30vs.120 m in/week).The potential clinical significance of reducing abdom inal fat has been highlighted by studies such as Rexrode etal.36who have reported a higher abdom inal adiposity being associated w ith an increased risk of coronary heart disease in a cohort of 44,702 female registered nurses aged 40—65.The estimated energy consumption over 8 h of soccer training(30 m in/week over 16 weeks)at an average HR of 155 bpm for untrained women would be in the area of 4000 kcal,corresponding to about 0.5 kg of fat.9It may therefore be speculated that fat oxidation was elevated outside the soccer training,as was found in other studies17which demonstrated a positive effect on cardiovascular and metabolic fi tness after 12—16 weeks of recreational soccer training,where an increase in the fat oxidation capacity at low to moderate exercise intensities, corresponding to the intensity during everyday life activity, was observed.Thatno equivalentoverallgroup fat losses were seen follow ing WBV training may well be due to the absence of an equivalent raising of the HR as observed during the soccer training.Other studies using oscillating27,28and vertical37WBV training have similarly reported no alterations in fat mass.Although WBV training has been reported to stimulate muscular work and to elevate metabolic rate to some extent,38the stimulus is probably insufficient to cause any change in fat mass for inactive premenopausal women.

4.2.Aerobic fitness

A fter 16-week of soccer training,the HR was on average 10 bpm lower in the last phase of a standardised submaximal YYIE1 test.A drop in HR loading during submaximalexercise indicatesan increase in aerobic fi tnessand isin accordancew ith findingsfrom previousstudiesusing recreationalsoccertraining for premenopausal women.HR was found to decrease by 10—20 bpm during walking and jogging at6—11 km/h after 16 weeks of tw ice-weekly 1-h soccer sessions for 20—45-year-old untrained women in conjunction with an increase in maximal oxygen uptake of15%,13,17and HR decreased by 7 bpm during submaximal cycling exercise after 12 weeks of training for tw ice-weekly 1-h soccer sessions for 25—65-year-old women, who had an increase in maximaloxygen uptake of5%over the course of training.14

The present study also indicated positive effects on muscular aerobic fi tness for the SG in comparison to the VG and the CO.The suggestion of an improvement in oxidative metabolism for the SG is reinforced by the recorded decrease in PCr depletion at the end of the ramp test at an equivalent time point,after the training intervention compared w ith the pre-training value.The changes observed for this parameter indicate that the training was of sufficient intensity to induce adaptive responses w ithin the muscle,either ata m itochondrial level via biogenesis or at a vascular level such that O2availability was improved.The fact that the relative PCr sparing is not the result of an increased contribution from glycolytic energy metabolism is confi rmed by no differences being recorded for end-exercise muscle pH.Thus,the inference is that a higher proportion of the energy demands during the ramp test were being met by oxidative mechanisms for the participants in the soccer group post-intervention,and hence that a greater oxidative capacity had been developed as a direct resultof the training.However,given the inactive nature of the population investigated,vascular changes cannot be ruled out as a potentially contributory factor.

4.3.BP

No changes in BP were observed in any of the groups in the present study.However,decreases in systolic(7—8 mmHg) and diastolic(4—5 mmHg)BP have been previously observed for normotensive premenopausal women and young normotensive men after 12—16 weeks of small-sided soccer played tw ice weekly for 1 h.8,17The lack of change in BP for any of the groups could therefore have been due to the small volume of training,which suggests that a minimum duration and intensity is required to induce a reduction in BP.18However,it should also be noted that the SG had baseline systolic pressures of 117 mmHg and diastolic pressures of 75 mmHg,and many participants had values below 115/75 mmHg,where further reductions follow ing exercise interventions have been shown to lim it health effects.39Further studies are required to elucidate whether small-volume soccer can be used to lower BP for participants w ith m ild to moderate hypertension.In line w ith some27but not all40previous studies,no changes were observed in BP after16 weeks of WBV training.The low HRs and implied lack of cardiovascular challenge may explain why BP did not change in the present intervention.Mechanisms behind the change in BP found in previous studies40have not been elucidated and further studies are needed to evaluate whether it was the dynamic nature of the exercises or the heavy load placed on the lower limbs which was associated w ith the positive impact on BP.

4.4.Limitations

The study has a number of limitations which may impact upon the conclusions subsequently drawn.One aspectwas that the net time actually spentexercising was potentially notequal for the SG and VG as soccer is an unpredictable,start-stop exercise modality,in contrast to the carefully regulated vibration protocol.However,one of the centralaims of the study was to compare health benefi ts of different training regimes, which took equivalent times to undertake,and so the time duration was kept constant between modalities rather than trying to ensure equivalent workloads.An additional concern was that the age range of the participants was also quite w ide. However,when age was included as a covariate within the analysis it did not affect the results found.A potentially more significant problem were changes in lifestyle that may have occurred over the relatively long intervention period.A lthough participants were asked to maintain their normal diet and PA, we were not able to directly control it.In particular,for the exercise groups it is notknown whether the soccerorvibration training resulted in a reduction in the time spent undertakingother PAs relative to before the beginning of the study,i.e., soccer or vibration training became a replacement activity, rather than an additional one on top of their pre-existing activities.

5.Conclusion

In summary,16 weeks of small-volume recreational soccer improved body composition,muscle PCr kinetics,and HR during submaximalexercise in inactive premenopausalwomen w ith no prior experience of soccer.Specifically,tw ice-weekly 15-m in sessions of soccer were sufficient to reduce fat percentage and fatmass of the trunk and android region.None of the above measures were altered after the WBV training.As such it provides evidence that more aerobically challenging exercise regimes such as small-volume,small-sided soccer training may be a more favourable choice for a training intervention for individuals w ith time constraints where weight loss and improvements in muscle oxidative capacity are of primary concern.

Acknow ledgments

The authors would like to thank the participants for their great efforts.We would also like to thank Rebecca Lear,Don Kim,and Jam ie Blackwell for excellent technical support. FIFA-Medical Assessments and Research Centre(F-MARC) and Nordea-fonden supported the study (No.1-ST-P-$$$-$$$-036-JZ-F1-05858).

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Received 21 February 2014;revised 19 May 2014;accepted 3 July 2014 Available online 7 August 2014

*Corresponding author.

E-mail address:j.fulford@exeter.ac.uk(J.Fulford)

Peer review under responsibility of Shanghai University of Sport.

2095-2546/$-see front matter CopyrightⒸ2014,Shanghai University of Sport.Production and hosting by Elsevier B.V.A ll rights reserved. http://dx.doi.org/10.1016/j.jshs.2014.07.003