Journal of Strength and Conditioning Research. 2007, 21(4), 1286-1290€) 2007 National Strength & Conditioning Association

ACUTE EFFECT OF TWO AEROBIC EXERCISE MODESON MAXIMUM STRENGTH AND STRENGTH ENDURANCE

EDUARDO OLIVEIRA DE SOUZA,' VALMOR TRICOLI,^ EMERSON FRANCHINI,^ANDERSON CAETANO PAULO,^ MARCELO REGAZZINI,^ AND CARLOS UGRINOWITSCH*

'Department of Sport, School of Physical Education and Sport, University of Sdo Paulo, Sdo Paulo, SP, Brazil;-College of Physical Education, Mackenzie University, Sdo Paulo, SP, Brazil.

ABSTRACT, de Souza, E.O., V. Tricoh, E. Franchini, A.C. Paulo,M. Regazzini, and C. Ugrinowitsch. Acute effect of two aerobicexercise modes on maximum strength and strength endurance.J. Strength Cond. Res. 21(4):1286-1290. 2007.—The purpose ofthis study was to evaluate the effects of 2 modes of aerobic ex-ercise (continuous or intermittent) on maximum strength (1 rep-etition maximum, IRM) and strength endurance (maximum rep-etitions at 80* of IRM) for lower- and upper-hody exercises totest the acute hypothesis in concurrent training (CT) interfer-ence. Eight physically active men (age: 26.9 ± 4.2 years; bodymass: 82.1 ± 7.5 kg; height: 178.9 ± 6.0 cm) were submitted to:(a) a graded exercise test to determine Vo^max (39.26 ± 6.95mlkg"'min ') and anaerobic threshold velocity (3.5 mmolL ')(9.3 ± 1.27 km-h '); (b) strength tests in a rested state (control);and (c) 4 experimental sessions, at least 7 days apart. The ex-perimental sessions consisted of a 5-kilometer run on a treadmillcontinuously (90% ofthe anaerobic threshold velocity) or inter-mittently 11:1 minute at Vo^max). Ten minutes after the aerohicexercise, either a maximum strength or a strength endurancetest was performed (leg press and hench press exercises). Theorder of aerobic and strength exercises followed a William'ssquare distribution to avoid carryover effects. Results showedthat only the intermittent aerobic exercise produced an acuteinterference effect on leg strength endurance, decreasing signif-icantly (p < 0.05) the number of repetitions from 10.8 ± 2.5 to8.1 ± 2.2. Maximum strength was not affected by the aerobicexercise mode. In conclusion, the acute interference hypothesisin concurrent training seems to occur when both aerohic andstrength exercises produce significant peripheral fatigue in thesame muscle group.

KEY WORDS, concurrent training, fatigue

INTRODUCTIONm any sports require simultaneous expressionof strength and endurance abilities. Due tothis fact, athietes incorporate strength andendurance exercises into their training rou-tines. However, training both strength and

endurance may produce interference effects, reducing themagnitude of training adaptations and performance in-crements (2, 3, 7, 8, 15). Several studies have indicateddecreased strength gains with this type of training (6, 7,9), which is usually called concurrent training (CT). Thesestudies have suggested 3 hypotheses to explain thestrength development impairment: (a) the chronic hy-pothesis, which states that some adaptations caused byendurance training are antagonist to strength trainingadaptations (10); (b) the overtraining hypothesis, which.suggests that concomitant volume increments in both en-durance and strength training loads may cause overtrain-ing syndrome (10); and (c) the acute hypothesis in whichan endurance training, performed prior to a strength

training in the same training session, would produce re-sidual fatigue, compromising force production during thestrength training session (9).

Craig et al. (6) were the first to propose an acute in-terference effect to explain the CT phenomenon. Theystated that there is an acute fatigue effect from a previousendurance exercise on strength exercise performance (1,6t. The acute peripheral fatigue from the endurance ex-ercise would then reduce the ability of skeletal musclesto produce tension (4). Some authors have suggested thatthe degree of muscle tension is critical for strength gains.Thus, any exercise that decreases the ability of the mus-cles to produce tension will lead to submaximal strengthdevelopment (1, 6, 9).

Particularly, the studies that tested the acute hypoth-esis produced controversial results (1, 6, 9, 11). Sporerand Wenger (17) observed a significant strength endur-ance decrement after 36 minutes of continuous cycling at70% ofthe maximum aerobic power, while Leveritt et al.(11) found no significant reduction in force production af-ter a 50-minute exercise in a cycloergometer at 70-110%of the critical power.

In a review paper, Docherty and Sporer (7) proposedthat this acute interference phenomenon is present onlywhen aerohic and strength exercises are both dependenton peripheral or central mechanisms. Thus, if the inten-sity of an aerobic exercise is high enough to deplete mus-cle glycogen content, then strength endurance perfor-mance will be greatly affected. On the other hand, max-imum strength will not be significantly affected becauseit relies more in the neural drive for force production thanin the muscle fiher force generation capacity and glycogenstore. Thus, it is not known if the combination of endur-ance and strength exercises in a training session, stress-ing either central or peripheral mechanisms, producesgi'eater interference effects than a session in which thiscombination alternates stress over peripheral and centralmechanisms.

Another explanation to interference may be the motorunit pool activated during both exercises. Small motorunits are predominantly recruited in low force contrac-tions. As the force level increases, larger motor units com-posed of fast twitch fibers are also recruited (size princi-ple). Low-intensity aerobic training sbould then recruitonly slow motor units due to the low force requirement.On the other hand, high-intensity aerobic training (>90%Vo^max) should activate both small and large motorunits. In the same way, low-intensity strength workoutactivates mainly small motor units, while strength train-ing above 709f of 1 repetition maximum (IRM) requires

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AEROBIC EXERCISE AND STRENGTH 1287

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FIGURE 1. Overview of experimental sessions. A: Warm-up.B: Aerobic exercise, either continuous or intermittent. C: Pas-sive recovery. D: Strength tests, either 1 repetition maximumURM) or strength endurance. E; Passive recovery. F: Strengthupper-body tests, either IRM or strength endurance.

the activation of both small and large motor units. Thus,Nelson et al. (12) proposed that strength training and en-durance training could activate the same motor unit pooland then maximize the acute interference phenomenon.

The aim of this study was to evaluate if the hypothesisdeveloped by Docherty and Sporer (7) for CT interferenceeffect is valid when both aerobic and strength exercisesstress peripheral mechanisms, in a practical context.

M E T H O D S

Experimental Approach to the ProhlemThis study was designed to investigate if CT interferenceis caused only when both aerobic and strength exercisesstress peripheral mechanisms, as proposed by Dochertyand Sporer (7). Thus, we tested the effects of 2 modes ofaerobic exercise, continuous (below anaerobic threshold),which should stress central mechanisms, and intermit-tent (1:1 minute at VO;imax) to stress peripheral mecha-nisms, on maximum strength (central) and strength en-duiance (peripheral) for lower- and upper-body exercises.

SuhjectsEight physically active male subjects were selected toparticipate in this study. Their mean (± SD) age, bodymass, height, VO;imax, and anaerobic threshold velocity(3.5 mmol-L ') were 26.9 (± 4.2) years, 82.1 (± 7.5) kg,178.9 (± 6.0) cm, 39.26 (± 6.95) mlkg '-min ', and 9.3(± 1.3) km-h \ respectively. They had 4.1 years of resis-tance training experience on average and exercised 1-3times per week with loads 50-80% of IRM. In addition,subjects had on average 4.2 years of participation insports at a recreational level, 1-3 times per week. Sub-jects were screened for cardiovascular disorders throughPar-Q and electrocardiographic records during theVo^max test. The study was approved by the University'sethic committee, and all subjects signed an informed con-sent form before participation.

Experimental DesignThe study consisted of a randomized crossover design, inwhich all subjects completed both control and experimen-tal conditions. Each session was 1 week apart to avoidany carryover effect (Figure 1).

Familiarization Session

The anaerobic threshold and Vo. max were assessed onthis session. Subjects performed a progressive runningspeed test until voluntary exhaustion on a treadmill.Each stage lasted 3 minutes. The initial speed was set at(i.O km-h ', and was increased 1 km-h ' per stage untiltbe subject could no longer continue. The O uptake wasmeasured throughout the test and the average of 3 larg-est values was defined as VOamax (K4b^ Cosmed, Rome,

Italy). The maximal velocity reached in the test, was de-fined as Vo^max. At the end of each stage, a 25 (xl bloodsample from the left ear lobe was collected in heparinizedcapillary tubes and stored in Eppendorfs. Blood lactateconcentration was measured by electrochemical tech-nique (Yellow Springs 1500 Sport, Yellow Springs, OH)after sodium fluoride stabilization (4.7 mM). One mmolabove resting values and 3.5 mmol lactate concentrationswere interpolated from the raw data to estimate lactateand anaerobic threshold velocities, respectively. Subjectsinformed their rates of perceived effort (RPE) at the endof each stage. In addition, heart rate was monitored usinga heart rate monitor (Polar Vantage NV, Electro Oy, Fin-land). After the Vo^max test, subjects were familiarizedwith the strength tests in the inclined (45 ) leg press andin the bench press, and a gross estimate of the subject'sIRM was obtained. The body position of the subjects inboth exercises was defined and recorded for next famil-iarization and experimental sessions as follows:

Inclined Leg Press. Subjects were seated in the ma-chine and placed both feet on the plate in a self-selectedposition. The area of the plate was divided into 10 cmsquares to help record the feet location. Then, the ma-chine was unlocked and the plate was lowered (or lifted)until a knee angle of 90" was obtained. Then, the positionof the plate was defined in a measuring tape placed onthe side ofthe sliding track. A plastic device was insertedin a 90° angle with the track to ensure correct positionduring each exercise repetition. The repetition started atcomplete knee extension; tbe subject lowered the plateuntil the specified height on the track, and then returnedto full extension.

Bench Press. Subjects lay on the bencb in a supineposition with the shoulders under the bar and both feeton the ground. Then, subjects gripped the bar in a com-fortable position. The distance of both thumbs from thecenter of the bar was recorded in a measuring tape placedover the bar. The repetition started in full elbow exten-sion, the bar wa.s lowered up to touching tbe chest, andthe repetition finished returning to full extension.

Control SessionsIn the first control session the IRM values for both ex-ercises were determined, first for the inclined leg pressand then for the bench press. The amount of weight usedin the first repetition was defined as 8O'/( of the weightlifted in the first familiarization session for each exercise.Then, subjects had up to 5 trials to reach maximum loadwith a 3-minute interval between trials. There was a 5-minute interval between exercises.

In the second control session subjects performed thestrength endurance test. They had to perform as manyrepetitions as possible with a load of 80% of the IRM inhoth exercises.

Experimental SessionsSubjects performed 4 experimental sessions consisting ofa 5-kilometer run on a treadmill continuously (CONT)(90% of the anaerohic threshold velocity, 8.1 ± 1.1km-h"') or intermittently (INT) (1:1 minute at Vo^max,12.6 ±1.5 km h '). Ten minutes after the aerobic exerciseeither a maximum strength (IRM) or a strength endur-ance test was performed (leg press and bench press ex-ercises). Thus, the 4 experimental sessions were: contin-uous run and maximum strength (CM), continuous runand strengtb endurance (CE), intermittent run and max-imum strength (IM), and intermittent run and strength

1288 DE SOUZA, TRICOLI, FRANCHINI ET AL.

400 n

250Control Continuous Intermittent

FIGURE 2. Maximum strength (kg) for the leg press exercise.

D>

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CC

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110-

100 -

90 -

80-

70-

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Control Continuous Intermittent

FIGURE 4. Maximum strength (kg) for the hench press exer-cise.

endurance (IE). The experimental sessions were at least7 days apart. The order of the experimental sessions fol-lowed a William's square distribution to avoid carryovereffects.

Statistical AnalysesA mixed model was performed having aerobic exercisemodality (control, continuous, and intermittent) as a fixedfactor and subjects as a random factor, for both responsevariables, maximum strength and strength endurance,for each exercise. Whenever a significant F value was ob-tained a post-hoc test with a Tukey adjustment was per-formed for multiple comparison purposes. Significancelevel was set a tp < 0.05.

RESULTS

The continuous protocol produced no interference effectin either maximal strength or strength endurance forboth leg press and bench press exercises (Figures 2, 3,and 4). On the other hand, the intermittent run produceda significant reduction only in leg press strength endur-ance (from 10.8 ± 2.5 to 8.1 ± 2.2 repetitions, p = 0.03)

(Figure 5), but there was also a trend to decrease lowerlimb maximum strength ip = 0.07).

DISCUSSION

The purpose of this study was to evaluate the acute efFectof 2 aerobic exercise modes, CONT and INT, on maximumstrength and strength endurance on both the lower andupper body. The main finding of this study was that theINT reduced significantly lower-hody strength enduranceand nonsignificantly maximum strength.

The CONT aerobic exercise i^O'Yc anaerobic thresholdvelocity) affected neither maximal strength nor strengthendurance, which is in disagreement with some previousstudies. Ahernethy (1) had a group that performed con-tinuous aerobic exercise for 150 minutes at 35'> of peakcycle ergometer oxygen consumption and found a small,but significant (4^) decrement in knee extension peaktorque. Sporer and Wenger (17) also observed a signifi-cant strength endurance decrement after 36 minutes ofcontinuous cycling at 70% ofthe maximum aerobic power.On the other hand, Leveritt et al. (11) found that strength

14

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6 -

4 -

2 -

Control Continuous Intermittent

FIGURE 3. Strength endurance (repetitions) for the benchpress exercise.

14 H

12

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4 -

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Control Continuous Intermittent

FIGURE 5. Strength endurance (repetitions) for the leg pressexercise. * Significantly smaller than control condition ip =0.03).

AEROBIC EXERCISE AMD STRENGTH 1289

was not reduced after aerohic exercise in a cycle ergom-eter (50 minutes at 70-110% ofthe critical power). Thedifference between our results and the results ofthe stud-ies that found interference may be attributed to the aer-ohic exercise performed in a cycle ergometer, which is be-lieved to produce a greater stress upon the lower limhmuscles than a running exercise. In addition, the studythat did not find interference ofthe aerohic hike protocolonly evaluated strength 8 hours after exercise completion(12). Tbis time window may be large enougb to producefull strength recovery. Thus, the interference produced bylow-intensity aerobic exercise seems to occur wben it re-quires greater force production tban in running.

Tbe INT produced a significant reduction in lower-body strengtb endurance (p ^ 0.03). The mean numberof repetitions after INT protocol decreased significantlyfrom 10.8 ± 2.5 to 8.1 ± 2.2. Sporer and Wenger (18) alsofound tbat tbe number of repetitions performed over 4sets in tbe leg press decreased significantly (48 ± 3 SEvs. 36 ± 3 SE], 4 hours after intermittent aerobic exer-cise. Leveritt and Abernetby (11) reported a reduction intbe number of repetitions in tbe squat exercise in the firstset when performed 30 minutes after intermittent aerobicprotocol (13.83 ± 5.71 vs. 8.83 ± 2.89). All tbese resultssupport tbe acute bypothesis proposed by Craig et al. (6).In addition, Docberty and Sporer (7) proposed tbat theacute interference phenomenon occurs only when high-intensity intermittent aerohic training (>90% Vo. max) isperformed concurrently witb resistance training of 8 to12RM. Sale (14) described tbat fast motor units are ac-tivated in running activities performed close to Vo. max.During strength endurance exercise we should expecttbat not all motor units are recruited. However, fast mo-tor units bave a low resistance to fatigue and are not ableto keep activated for a long period of time. Then, freshfast motor units bave to be recruited to keep force pro-duction. This phenomenon is defined as motor unit sub-stitution (19). Tberefore, it is expected tbat tbe majorityof tbe available motor units are recruited during strengtbendurance exercise, which have also been activated dur-ing tbe intermittent aerobic exercise.

Probably, not only motor unit recruitment but otherfactors such as accumulation of metabolites could explaintbe acute interference pbenomenon during concurrenttraining. Wben a bigh-intensity aerobic exercise is per-formed, part of tbe energy requirement is produced byglycolysis, wbicb bas metabolic end products (lactate, H',ADP/AMP, P,). Sucb metabolites are tbought to impairenergy production and hence force generation (5, 13, 18).Moreover, exercise characteristics may infiuence produc-tion of metabolites. Smilios et al. (16) described bigherblood lactate accumulation after strength endurance tbanmaximum strengtb exercise.

In our study, the decrease in maximal strengtb almostreacbed significance (p - 0.07) after INT. Tbis findingdemonstrates tbat tbe INT had tbe potential to decreasemaximal strengtb. Bentley et al. (4) sbowed tbat maximalisometric force of tbe quadriceps was decreased 6 hoursafter exbausting intermittent aerobic exercise. In order toproduce a maximum strengtb repetition (IRM) all avail-able motor units have to be recruited, but tbey will befatigued from tbe previous aerobic exercise. Tbus, wecould also expect a decreased maximum strengtb perfor-mance. A greater sample size may bave produced a sig-nificant decrement in force production. Taking the trendtowards a decreased maximum strength and tbe theorybebind motor unit activation togetber, we may say tbat

our data do not corroborate tbe bypotbesis proposed byDocherty and Sporer (7).

Tbe otber finding was that aerobic exercise affectedonly tbe muscles involved in tbis activity. Neither upper-body maximal strengtb nor strengtb endurance was af-fected by the CONT or tbe INT aerobic exercise. Only 1study examined tbe acute effect of an aerobic exercise intbe ability to exert force in a muscle group not exercisedduring this activity. Sporer and Wenger (17) found tbattbe average repetitions over 4 sets of a strengtb exercisewere not affected by eitber continuous or intermittentaerobic exercise. Tbese data demonstrated that tbe inter-ference effect is caused mainly hy peripheral factors (pe-ripheral fatigue). Thus, we may say that aerobic trainingdoes not afTect strength in the muscles not exercised dur-ing aerobic activity.

In conclusion, our study demonstrated tbat only INTdecreased tbe numher of repetitions in strength endur-ance and presented a potential to produce interference inmaximal strengtb in tbe muscles involved in hoth tasks.The CONT protocol interfered in neither maximalstrengtb nor strength endurance.

PRACTICAL APPLICATIONS

Our results indicate that both maximum strength andstrength endurance may he trained afler a continuouslow-intensity and moderate duration aerohic exercise,since there is no acute interference effect. On tbe otberhand, if the main goal of tbe training session is to developeitber maximum strengtb or strengtb endurance, theyshould be performed before an intermittent aerobic ex-ercise at Vo^max. Tbis aerohic exercise may produce fa-tigue and impair strength development.

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Address correspondence to Dr. Carlos Ugrinowitsch,ugrinowi@usp.br.