Baixe o app para aproveitar ainda mais
Prévia do material em texto
See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/6820634 The effects of varying time under tension and volume load on acute neuromuscular responses ARTICLE in ARBEITSPHYSIOLOGIE · NOVEMBER 2006 Impact Factor: 2.19 · DOI: 10.1007/s00421-006-0297-3 · Source: PubMed CITATIONS 32 READS 397 3 AUTHORS, INCLUDING: David Docherty University of Victoria 40 PUBLICATIONS 845 CITATIONS SEE PROFILE David Behm Memorial University of Newfoundland 214 PUBLICATIONS 4,124 CITATIONS SEE PROFILE Available from: David Behm Retrieved on: 28 October 2015 Eur J Appl Physiol (2006) 98:402–410 DOI 10.1007/s00421-006-0297-3 ORIGINAL ARTICLE The eVects of varying time under tension and volume load on acute neuromuscular responses Quan T. Tran · David Docherty · David Behm Accepted: 22 August 2006 / Published online: 13 September 2006 © Springer-Verlag 2006 Abstract The purpose of this study was to examine the eVects of diVerent methods of measuring training volume, controlled in diVerent ways, on selected vari- ables that reXect acute neuromuscular responses. Eighteen resistance-trained males performed three fatiguing protocols of dynamic constant external resistance exercise, involving elbow Xexors, that manipulated either time-under-tension (TUT) or vol- ume load (VL), deWned as the product of training load and repetitions. Protocol A provided a standard for TUT and VL. Protocol B involved the same VL as Protocol A but only 40% concentric TUT; Protocol C was equated to Protocol A for TUT but only involved 50% VL. Fatigue was assessed by changes in maxi- mum voluntary isometric contraction (MVIC), inter- polated doublet (ID), muscle twitch characteristics (peak twitch, time to peak twitch, 0.5 relaxation time, and mean rates of force development and twitch relax- ation). All protocols produced signiWcant changes (P · 0.05) in the measures considered to reXect neu- romuscular fatigue, with the exception of ID. Fatigue was related to an increase in either TUT or VL with greater fatigue, as reXected by MVIC and peripheral measures, being associated with diVerences in TUT. The lack of change in ID suggests that fatigue was more related to peripheral than central mechanisms. It was concluded that the load and contraction veloci- ties of the repetitions have diVerent eVects on acute neuromuscular responses and should, therefore, be clearly calculated when describing training volume for dynamic constant external resistance exercise training. Keywords Contractile properties · Contraction velocity · Central · Peripheral · Fatigue Introduction Resistance training is an eVective method for develop- ing muscular strength and hypertrophy. However, the optimal resistance training program and the relation- ship between the training variables and neuromuscular adaptation remain elusive. The diYculty in optimizing a resistance training program may be due to its com- plex nature, which can be attributed to the many train- ing variables that can be manipulated. The training variables include the load that is lifted, the volume and frequency of training, speed of contraction, work to rest ratios, fatigue, and the order in which the exercises are performed, as well as the interaction that may exist between these variables. Volume is considered to be one of the most important training variables, especially in regard to hypertrophic adaptations (Byrd et al. 2005) as well as improvements in force generation (Munn et al. 2005; Sclumberger et al. 2001). However, not all studies have found a signiWcant relationship between training volume and subsequent neuromuscu- lar adaptations (Hass et al. 2000; Carpinelli and Otto 1998). Q. T. Tran University of Queensland, Brisbane, QLD, Australia D. Docherty (&) School of Physical Education, University of Victoria, Victoria, BC, Canada V8W 3P1 e-mail: docherty@uvic.ca D. Behm Memorial University, St Johns’, NF, Canada 123 Eur J Appl Physiol (2006) 98:402–410 403 One explanation for the equivocal Wndings may be related to diVerences in the way training volume has been calculated. One common method for calculating training volume is to count the total number of repeti- tions completed during a speciWed training period. An alternative method is to describe volume in regard to the amount of work performed. Mechanical work is calculated by multiplying the force required to move the load, or resistance, by the distance traveled by the load. With the assumption that the force involved is equal to the load being lifted and that all repetitions are performed with the same range of motion, work may be approximated by multiplying the load by the number of repetitions, referred to as “volume load” (Stone et al. 1999). Measuring volume load may be a more precise way of calculating training volume because it recognizes that the load is a contributing fac- tor to volume. However, this method does not fully deWne the load and repetitions because similar volume loads may be obtained from diVerent combinations of load and number of repetitions. Potential discrepancies may arise also in describing training volume if the time the muscle is under tension (TUT) is diVerent or not controlled. To control for such discrepancies, volume may also be calculated as the cumulative time that the muscles are under tension during a training period. In order to quantify volume by TUT during dynamic training protocols, load and contraction velocities of the concentric and eccentric phases, as well as the duration of any isometric phase, of the repetitions should be included. Few studies have directly manipulated TUT as a training variable or compared the separate inXuences of TUT and volume load on neuromuscular adaptations. Therefore, the speciWc eVects of TUT in regard to neuromuscular adaptations are not well understood at this time. Training studies that have varied TUT by manipu- lating contraction velocities during resistance training programs have produced equivocal results. Wescott et al. (2001) found that subjects performing slow tempo (ST) training, resulting in 2.5 times greater concentric TUT, experienced a signiWcant 50% improvement in mean strength compared to subjects training with regu- lar tempo (RT). However, Keeler et al. (2001), using a similar experimental design, found RT produced greater gains in strength compared to ST (39 and 15%, respectively). However, it should be noted that there was a variation in the training loads between groups, which would impact the results. In both studies, greater strength improvements were associated with the group that trained with a greater load Thus, interpretation of TUT, when confounded by variance in load, must be made with some caution. Fatigue has been implicated in long-term neuro- muscular adaptations with greater fatigue being asso- ciated with increased strength and hypertrophy (Rooney et al. 1994; Schott et al. 1995). Insight into the eVects of diVerent methods of describing training volume on neuromuscular adaptation may be initially gained by monitoring the acute neuromuscular fatigue responses. Muscle fatigue is multi-factorial and consequently a number of deWnitions have been proposed. Within the context of the present study fatigue has been deWned as an exercised-induced reduction in force generating capabilities, which may be central or peripheral in origin. Central fatigue refers to a reduction in voluntary activation of muscle during exercise. Fatigue as a result of impairments in force generating capacities at or distal to the neuro- muscular junction has been termed peripheral fatigue (Gandevia 2001). Fatigue has also been deWned as a response that is less than the expected or anticipated contractile response for a given stimulation (MacIn- toshand Rassier 2002). Presently, the majority of studies and training programs describe volume using the volume load method. However, without inclusion of TUT, it is uncertain whether these studies or programs can con- Wdently state that volume is equated. Few studies have directly examined the eVects of TUT on dynamic constant external resistance (DCER) training and currently no study has directly compared the eVects of TUT and volume load on acute fatigue. If long-term enhancement of muscular strength and hypertrophy is related to both fatigue and volume of training, resis- tance-training programs should clearly describe the volume of training using TUT or volume load. There- fore, the purpose of this study was to identify the spe- ciWc eVects of TUT and volume load on acute neuromuscular markers of fatigue following single- arm elbow Xexions. Methods Participants Eighteen university-aged males participated in the study (age = 25.1 § 3.5 years; mass = 85.2 § 13.2 kg). All participants were strength trained and had a mini- mum of 1 year of upper body resistance training. Prior to participation, written consent was obtained and all participants were briefed on the purpose of the study and potential risks involved in participation. Approval of the study was granted by the University Human Research Ethics Committee. 123 404 Eur J Appl Physiol (2006) 98:402–410 Experimental design Participants performed three fatiguing protocols that manipulated either TUT or volume load while main- taining the same resistance or load that was lifted. After satisfactory completion of two familiarization sessions, participants performed each protocol, in ran- dom order, on separate days with approximately 48– 72 h between testing sessions. All sessions were super- vised and participants were asked to refrain from per- forming any resistance training targeting the elbow Xexors for the duration of the study. Familiarization session Following the initial rest period (5 min) participants performed a warm-up consisting of three sets of ten repetitions of DCER elbow Xexion, separated by 3 min rest periods, at a load of 50% of the estimated 10RM. All warm-ups during the familiarization sessions were performed using the training regimen of protocol A (see Table 1). Participants were then tested for their maximal muscle stimulus (MMS). The interpolated doublet technique (ITT) was performed to familiarize the subjects with the protocol. Testing of the 10RM was conducted 5 min after the ITT. Participants performed single-arm standing dumbbell curls of the dominant arm. Participants had their backs to the wall to maintain form. One complete repetition consisted of moving the arm through the full range of elbow motion. The participants were instructed to maintain a supinated grip, to avoid any extraneous body movement, and keep in time with a pre-set metronome throughout the test. All 10RM test- ing was performed using the repetition scheme of pro- tocol A. Participants started at an initial load of 75% of the estimated 1RM. The load was adjusted accordingly by 100 g to 2 kg increments to ensure a 10RM was obtained. Five-minute rest periods between 10RM attempts were provided to minimize fatigue. No partici- pants required more than three attempts. Following the 10RM test, the three diVerent training protocols were performed in random order at 50% of the 10RM. This was necessary to familiarize the partic- ipants with the various cadences associated with each protocol (Table 1). Five-minute rest periods were pro- vided between fatiguing protocols. Testing session Following an initial rest period of 5 min, the participants performed an identical warm-up, as in the familiarization session, but utilized the repetition scheme of the fatigue protocol being tested to provide participants with addi- tional practice with the timing of lifts. Maximal voluntary isometric contraction (MVIC), twitch contractile proper- ties, and interpolated doublet (ID), were measured before and after the fatiguing protocols. Twitch contrac- tile properties were measured immediately after each fatiguing protocol, whereas the ID was administered 1 min post-fatiguing protocol (Behm et al. 2002). Fatiguing protocols The various protocols were designed to manipulate either concentric TUT or volume load with respect to protocol A. Participants were instructed to keep time with a metronome set at the speciWc cadence for the protocol. In protocol B participants performed the same volume load but with only 40% of the concentric TUT compared to protocol A, whereas in protocol C participants performed 50% of the volume load with equal TUT compared to protocol A (see Table 1). Manipulation of the concentric phase was chosen to be consistent with other dynamic training TUT studies (Keeler et al. 2001; Wescott et al. 2001). Ninety percent of the 10RM load was used as the load for all fatiguing protocols to ensure the volume load was consistent between trials (Benson et al. 2006). All participants were able to complete the prescribed repetitions. Setup on the modiWed preacher curl The maximal muscle stimulus, ID, twitch contractile properties, and MVIC tests were performed on the Table 1 Repetition scheme for three fatiguing protocols Note: Asterisk (*) denotes volume load was calculated by multiplying number of repetitions by 90% (of 10RM). Example calculation of volume load for protocol A = 3 £ 10 £ 0.9 = 27 Protocol Sets Repetitions Concentric phase (s) Eccentric phase (s) Volume load* Total concentric TUT (s) Total eccentric TUT (s) A 3 10 5 2 27 150 60 B 3 10 2 2 27 60 60 C 3 5 10 4 13.5 150 60 123 Eur J Appl Physiol (2006) 98:402–410 405 modiWed preacher curl apparatus. The apparatus was adjusted so that the thighs of the participant were par- allel with the Xoor with a 90° angle at the knee. The chest was placed Xush against the arm rest pad. The arm was placed Wrmly against the pad of the preacher curl bench with the elbow placed at a 90° angle and the forearm fully supinated. The joint angles were mea- sured with a goniometer. To minimize extraneous body movement, metal clamps were lowered until they pressed Wrmly against the upper arm (Fig. 1). The height of each clamp was measured and recorded for each individual. The wrists of the participants were inserted into a wrist strap attached to the strain gauge. When subject positioning was satisfactory a standard force of 10N (resting tension) was set to eliminate slack in the wire connecting the strain gauge to the wrist straps. Maximal muscle stimulus (MMS) The MMS test was conducted to determine the electri- cal stimulus that was used during the measurement of twitch contractile properties and ID tests. Placement of the electrodes was designed to target the musculocuta- neous nerve. The cathode was lowered over the biceps brachii (midbelly) midway between the anterior edge of the deltoid and the proximal elbow crease with the elbow Xexed at 90°. The anode was placed over the dis- tal tendon in the elbow groove (Allen et al. 1998). Large electrodes (10 £ 5 cm2) were used to fully cover the belly of the biceps brachii (Behm et al. 2002). Stim- ulation was administered using a constant high voltage stimulator (Digitimer Ltd. Model DS7A). Participants were instructed to remain relaxed and close their eyes to prevent anticipation of the stimulus. Voltage was set at 100-V rectangular pulse with pulse duration of 50 �s and amperage was progressively increased (10 mA to 1 A) on consecutive trials until no further increase in twitch amplitude was detected. Force values, sampled at 2,000 Hz, were detected by a strain gauge (Omegadyne Ltd. Model 101–500, range 0–500 lbs), ampliWed (Biopac Systems Inc. MP100), and analyzed (Acknowledge 3.7, Biopac Systems Inc.). The minimum electricalstimulus that elicited the greatest muscle contractile force was considered the MMS. Interpolated doublet technique (ITT) The ITT was used to measure the extent of muscle acti- vation. Pre-ID consisted of two maximal contractions separated by 3 min rest periods and three submaximal contractions (75, 50, and 25% of MVIC), in random order, interspaced by 1 min rest periods. Post-ITT con- sisted of one MVIC followed by 1 min rest and three submaximal contractions (75, 50, and 25% of MVIC), in the same order as pre-ITT, interspaced by 30 s rest periods. The shorter post-ITT was used to minimize the eVects of recovery (Behm et al. 2002). Each con- traction was 3 s in duration, two doublets were deliv- ered at 1.5 and 3 s of the contraction. Participants were instructed to cease muscle contraction after the second doublet. A third doublet was delivered at rest follow- ing each contraction. A doublet was used (2 stimuli interspaced by 10 ms) to increase the signal to noise ratio (McKenzie and Gandevia 1991). All maximal and submaximal forces were plotted with their respective ID ratios. The ID ratio was expressed as the ID divided by the control doublet (doublet at rest). A second order polynomial equa- Fig. 1 Body position on the modiWed preacher curl appa- ratus from the side (a) and front (b) 123 406 Eur J Appl Physiol (2006) 98:402–410 tion was constructed (ax2 + bx + c) for each subject to determine the extent of muscle activation because it is considered by some authors to best represent the cur- vilinear relationship of voluntary force and muscle activation (Behm et al. 1996). The mean R2-values for the 2° polynomial equation for all pre- and post- fatiguing protocol measures were 0.97 and 0.95, respectively. Maximal voluntary isometric contraction Participants performed two MVICs, separated by 3 min rest periods, prior to the testing protocol and one MVIC following the testing protocol. The average of the peak pre-protocol MVIC forces was measured. Maximal voluntary isometric contractions were mea- sured 1 min after completion of the fatigue protocol. All MVIC attempts were 3 s in duration. Twitch contractile properties Participants were instructed to remain relaxed and to close their eyes to prevent anticipation of the stimu- lus to eliminate neural activation. All twitch con- tractile properties were measured from a single stimulation (singlet): Peak twitch (PT) force was recorded as the greatest force evoked by the singlet, Time to peak twitch (TPT) was the time from the onset of stimulation to the PT, and half relaxation time (0.5RT) was the time from PT to decrease in half the amplitude. The mean rate of force development (PT/TPT) is deWned as the average rate for peak force development evoked from the singlet in a rested state and was calculated by dividing the PT by TPT. Similarly the mean rate of twitch relaxation is deWned as the average rate for the PT to decrease in tension by half and was calculated by dividing ¡0.5PT by 0.5RT. All twitch characteristics were included (Acknowledge 3.7. Biopac Systems Inc.) and averaged (three trials). Statistics Data were analyzed using SPSS 11.5. A two-way analy- sis of variance (ANOVA) with repeated measures was conducted (3 £ 2). The two ANOVA levels included the fatigue protocols (A, B, and C) and the diVerences between pre- and post-tests measures. F ratios that reached P · 0.05 were considered signiWcant. Student’s paired t tests were performed, with a Bonferoni correc- tion, where signiWcant main eVects were detected. One set of values for the twitch contractile properties was removed due to incomplete data. Results Fatigue A signiWcant interaction was detected for isometric force development from the pre- to post-protocol val- ues (F = 4.73, P < 0.05). All protocols resulted in sig- niWcant decreases in peak isometric force output from pre- to post-protocol values (P < 0.05). Force produc- tion following protocol A, which involved high volume load and high TUT, decreased by 19.2 § 1.9% (mean § SEM), which was signiWcantly greater (P < 0.05) than force decrements observed in protocol B (decreased TUT) (¡12.8 § 1.6%). Protocol C, with a decreased volume load, resulted in a 15.0 § 2.8% reduction in force but was not signiWcantly diVerent from protocol A or B (Fig. 2). Neural measures No signiWcant interaction was detected for percent diVerence muscle activation from pre- to post-values between protocols (F = 0.67). Mean muscle activation values, across all protocols, indicated that participants were able to achieve full or near full motor unit recruit- Fig. 2 Maximal voluntary isometric contraction measured pre- and 1 min post-completion of each fatiguing protocol. Vertical lines represent standard error of the means. Asterisk (*) denotes signiWcant diVerence from pre- to post-completion (P < 0.05). Letter “a” denotes signiWcant percent diVerence from each other (P < 0.05) 200 250 300 350 400 450 A B C Fatigue Protocol M ax im al V ol un ta ry Is om et ric C on tra ct io n (N ) pre post * a * * a 123 Eur J Appl Physiol (2006) 98:402–410 407 ment (96.5 § 0.6%). Initial muscle activation of protocols A, B, and C (95.7 § 1.3, 96.5 § 0.73, and 97.3 § 0.85%, respectively) were not signiWcantly diVerent from post-protocol values (95.1 § 1.54, 97.3 § 0.70, and 96.2 § 1.1, respectively). Peripheral measures A signiWcant interaction was found for the twitch con- tractile properties (F = 5.01, P < 0.05). The high vol- ume load and high TUT of protocol A resulted in signiWcantly greater (P < 0.05) percent reduction in PT (¡57.2 § 5.1%) than protocol B and C (¡11.8 § 6.5 and ¡30.3 § 8.6%, respectively). Protocol C, which involved 2.5 times greater concentric TUT, resulted in signiWcantly greater percent decreases in PT compared to protocol B (P < 0.05) (Fig. 3). No signiWcant interaction occurred between the fatiguing protocols in TPT or 0.5RT but there was a signiWcant main eVect from the pre- to post-protocol values (F = 33.5, P < 0.05 and F = 3.6, P < 0.05, respec- tively). Therefore, all protocols resulted in similar deceases from pre- to post-protocol values in TPT (¡18.4 § 3.13, ¡16.6 § 2.2, and ¡20.1 § 3.35%, respectively) and 0.5RT (¡37.5 § 8.8, ¡33.1 § 7.1, and ¡30.2 § 7.0%, respectively) (Figs. 4, 5). A signiWcant interaction was detected for the mean rate of force development (F = 4.51, P < 0.05). The Fig. 3 Peak twitch forces measured pre- and post-completion of each fatiguing protocol. Vertical lines represent standard error of the means. Asterisk (*) denotes signiWcant diVerence from pre- to post- (P < 0.05). Letter “a” denotes signiWcant percent diVerences from each other (P < 0.05) 0 5 10 15 20 25 30 35 40 A B C Fatigue protocol Pe ak T w itc h (N ) pre post * a * a * a Fig. 4 Time to peak twitch measured, pre- and post-completion of each fatiguing protocol. Vertical lines represent standard error of the means. All protocols showed similar signiWcant decreases between the pre- and post-conditions 0 20 40 60 80 100 120 A B C Fatigue Protocol Ti m e to P ea k Tw itc h (m s) pre post Fig. 5 Half relaxation time measured pre- and post-completion of each fatiguing protocol. Vertical lines represent standard error of the means. All protocols showed similar signiWcant decreases between the pre- and post-conditions 0 10 20 30 40 50 60 70 80 90 100 A B C Fatigue Protocol H al f R el ax at io n Ti m e (m s) pre post 123 408 Eur J Appl Physiol (2006) 98:402–410 mean rate of force development for protocol A decreased by 45.9 § 6.6%, which was signiWcantly diVerent (P < 0.05)than protocol B (8.64 § 9.4%) and C (¡12.8 § 10.5%). Protocol B and C were not signiW- cantly diVerent. Protocol B was not signiWcantly diVer- ent from pre- to post-protocol values (Fig. 6). A signiWcant interaction was detected for the mean rate of twitch relaxation (F = 4.01, P < 0.05). The mean rate of twitch relaxation of protocol A decreased by 20.3 § 8.3% and was signiWcantly diVerent (P < 0.05) compared to the increased rates observed from B (74.5 § 32.7%) and C (6.3 § 11.8%). Protocol B and C were statistically diVerent (p < 0.05). Protocol C was not signiWcantly diVerent from pre- to post-protocol values (Fig. 7). Discussion The major Wnding of the study was that manipulating TUT or volume load inXuenced acute markers of fatigue when equated for volume (either by the TUT or volume load method). Greater concentric TUT, when volume load was equated, resulted in signiW- cantly greater neuromuscular fatigue (A vs. B). Sub- stantially greater impairments to twitch force suggest greater training stresses are placed on the peripheral (muscle) rather than the central nervous component with a longer TUT (A and C vs. B). Similarly, more volume load resulted in signiWcantly greater peripheral fatigue, as reXected by evoked muscle twitch measure- ments, when TUT was equated (A vs. C). Therefore, resistance training programmes or protocols that fail to control for either volume load and TUT cannot conW- dently assume that volume is equated. Muscle contractile properties Varying TUT Twitch contractile properties exhibited signiWcant interactions with diVerent TUT. The greater concentric TUT from performing protocol A, which was 2.5 times greater than protocol B, resulted in a signiWcantly greater percent decrease in PT suggesting greater impairment of muscle contractile properties. Accord- ing to Ingalls et al. (1998) the majority of immediate deWcits in twitch force production may be attributed to impairments within the excitation–contraction-cou- pling processes. The data are consistent with Behm et al. (2002) who observed greater PT deWcits following a fatiguing protocol that involved four times the TUT than another protocol. Performing all protocols resulted in signiWcant decreases in TPT and 0.5RT from initial values but no Fig. 6 Mean rate of force development measured pre- and post- completion of each fatiguing protocol. Vertical lines represent standard error of the means. Asterisk (*) denotes signiWcant diVerence from pre- to post-completion (P < 0.05). Letters “a” and “b” denote signiWcant percent diVerences from each other (P < 0.05) 0 50 100 150 200 250 300 350 400 450 A B C Fatigue Protocol M ea n R at e of F or ce D ev el op m en t ( N/ s) pre post * b * ab a Fig. 7 Mean rate of twitch relaxation measured pre- and post- completion of each fatiguing protocol. Vertical lines represent standard error of the means. Asterisk (*) denotes signiWcant diVerence from pre- to post- (P < 0.05). Letter “a” denotes signiW- cant percent diVerence from each other (P < 0.05) -350 -300 -250 -200 -150 -100 -50 0 A B C Fatigue Protocol M ea n R at e of T w itc h Re la xa tio n (N /s ) pre post * a * a a 123 Eur J Appl Physiol (2006) 98:402–410 409 interactions were detected between protocols. These results were unexpected because temporal twitch char- acteristics are usually lengthened due in part to dis- rupted Ca++ kinetics as a consequence of fatigue (Ingalls et al. 1998; Ørtenblad et al.2000). The lack of signiWcant interaction of TPT and 0.5RT, despite diVer- ent fatigue responses, might be attributed to the signiW- cantly diVerent post-PTs (P < 0.01) of protocol A and B (Fig. 3). Behm et al. (2002) also detected signiWcant reductions in TPT and 0.5RT following a bout of resis- tive exercises. However, the large magnitude of PT deWcits (44.1–46.8%), similar to the present study, may have contributed to the decreased TPT. Behm and St- Pierre (1997) found that increased PT resulted in increased TPT and vice versa, thus, TPT and 0.5RT can interact with and be inXuenced by twitch amplitude. DiVerences may be present when TPT or 0.5RT are normalized to their respective PT. SigniWcant interac- tions were detected between protocols A and B when the mean rates of force development and twitch relaxa- tion were calculated, which may be a superior measure than TPT or 0.5RT because it addresses the potential problem of varying PT. The greater decreases in mean rates of force devel- opment and twitch relaxation after performing proto- col A, compared to protocol B, suggest disturbances in the rate of contractile property characteristics. The non-signiWcant change in mean rate of force develop- ment from pre- to post-protocol in performing protocol B suggest no temporal impairment, which is consistent with the minimal fatigue that was found. However, protocol B resulted in a signiWcant increase in the mean rate of relaxation (74.5 § 32.74%) suggesting the con- tractile mechanisms may be more eYcient. The increased rate of 0.5RT may be due to potentiation as a result of the less fatiguing protocol. Behm and St- Pierre (1997) found that isometric fatigue of the plan- tar Xexors resulted in potentiated twitch contractile properties. Garland et al. (2003) suggested that the mechanisms of fatigue and potentiation can coexist, and it is possible to have an increased rate of Ca++ reuptake at the sarcoplasmic reticulum (SR) despite an overall decrease in force output. Varying volume load Twitch contractile properties were also inXuenced by volume load. Performing protocol A, which involved twice the volume load compared to performing proto- col C, resulted in a greater reduction in PT. Conse- quently, performing protocol A may have produced greater impairments in muscle contractile properties. No signiWcant diVerences in TPT and 0.5RT were detected between protocols A and C. However, per- forming protocol A resulted in signiWcantly greater reduction in mean rates of force development and twitch relaxation than C, which suggests that greater decreases in PT may be a result of time-related con- tractile properties. Therefore, performing a greater volume load, when TUT and load were equated, resulted in greater deWcits in contractile properties. Volume load versus TUT Comparisons between performing protocols B and C suggest that varying TUT was more inXuential on acute peripheral fatigue than volume load when training load was equated. Reduction in PT following protocol C was signiWcantly greater than B, which suggests that the observed trends of greater fatigue may be a result of greater disruption in contractile properties. The signiWcant changes in twitch contractile proper- ties despite non-signiWcant changes in MVIC may be a result of low frequency fatigue (LFF), which is more consistent with human voluntary exercise (Jones 1996). Low frequency fatigue results in preferential muscle force impairment at low frequency stimulation whereas maximal strength production remains intact or is mini- mally impaired. Increased motor unit discharge has been proposed to partially explain maintenance of force production following post-exercise development of LFF (de Ruiter et al. 2005). This mechanism is con- sistent with the non-signiWcant changes in central fatigue observed in the present study. Extent of full activation All participants were able to achieve full or near full muscle activation (96.5 § 0.56%) of the elbow Xexors. These results agree with other studies that have reported high levels of muscle activation of the elbow Xexors (Allen et al. 1998 [99.1%]; Gandevia et al. 1998 [98%]). All fatiguing protocols resulted in non-signiW- cant changes in muscle activationand are consistent with other studies (Gandevia et al. 1998; Plaskett and Cafarelli 2001). The results suggest that within the con- text of the present study full or near full muscle activa- tion can be maintained during the development of fatigue during dynamic eVorts of the elbow Xexors. Conclusion Manipulating the TUT or the volume load during dynamic resistance training inXuences acute fatigue which may have an impact on chronic neuromuscular 123 410 Eur J Appl Physiol (2006) 98:402–410 adaptations. The majority of force deWcits appear to be due to peripheral rather than central factors. The data suggest that full muscle activation can be maintained during the development of fatigue of the elbow Xexors. Increased TUT or volume load resulted in greater fatigue that would appear to be a result of impairments in muscle contractile properties. The results of this study suggest that, in order to clarify the inXuence of resistance-training protocols, the load and contraction velocities of the repetitions for the exercise must be clearly deWned when describ- ing training volume. The diVerences in the acute neu- romuscular responses to the way training volume is manipulated may lead to diVerences in chronic neuro- muscular adaptations. If neuromuscular fatigue is an important variable in the development of muscular strength and hypertrophy, then greater TUT may yield superior strength and hypertrophic gains as long as the training load is not severely compromised. References Allen GM, McKenzie DK, Gandevia SC (1998) Twitch interpola- tion of the elbow Xexor muscles at high forces. Muscle Nerve 21:318–328 Behm DG, Reardon G, Fitzgerald J, Drinkwater E (2002) The eVect of 5, 10, and 20 repetition maximums on the recovery of voluntary and evoked contractile properties. J Strength Cond Res 16:209–218 Behm DG, St-Pierre DM (1997) EVects of fatigue duration on muscle type and voluntary and evoked contractile proper- ties. J Appl Physiol 82:1654–1661 Behm DG, St-Pierre DM, Perez D (1996) Muscle inactivation: assessment of the interpolated twitch technique. J Appl Physiol 81:2267–2273 Benson C, Docherty D, Brandenburg J (2006) Acute neuromus- cular responses to resistance training performed at 100% and 90% of 10RM. J Sc Med Sports 9:135–142 Byrd SK, Tarpenning KM, Marino FE (2005) Designing resis- tance training programmes to enhance muscular Wtness. Sports Med 35:841–851 Carpinelli RN, Otto RM (1998) Strength training: single set ver- sus multiple sets. Sports Med 26:73–84 de Ruiter CJ, Elzinga MJH, Verdijk PWL, van Mechelen W, de Haan A (2005) Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle. Eur J Appl Physiol 94:659– 559 Gandevia SC (2001) Spinal and supraspinal factors in human muscle fatigue. Physiol Rev 81:1725–1789 Gandevia SC, Herbert RD, Leeper JB (1998) Voluntary activa- tion of human elbow Xexor muscles during maximal concen- tric contractions. J Physiol 512:595–602 Garland SJ, Walton D, Ivanova TD (2003) EVect of force level and training status on contractile properties following fa- tigue. Can J Appl Physiol 28:93–101 Hass CJ, Garzarella L, De Hoyos D, Pollock ML (2000) Single versus multiple sets in long-term recreational weightlifters. Med Sci Sports Exer 32:235–242 Ingalls CP, Warren GL, Williams JH, Ward CW, Armstrong RB (1998) E-C coupling failure in mouse EDL muscle after in vivo eccentric contractions. J Appl Physiol 85:58–67 Jones DA (1996) High- and low-freqeuency fatgue revisited. Acta Physiol Scand 156:265–270 Keeler LK, Finkelstein LH, Miller W, Fernhall B (2001) Early- phase adaptations of traditional-speed vs. superslow resis- tance training on strength and aerobic capacities in sedentary individuals. J Strength Cond Res 15:309–314 MacIntosh BR, Rassier DE (2002) What is fatigue? Can J Appl Physiol 27:42–55 McKenzie DK, Gandevia SC (1991) Recovery from fatigue of hu- man diaphragm and limb muscles. Resp Physiol 84:49–60 Munn J, Herbert RD, Hancock MJ, Gandevia SC (2005) Resis- tance training for strength: eVect of number of sets and con- traction speed. Med Sci Sports Exer 37:1622–1626 Ørtenblad N, Sjøgaard G, Madsen K (2000) Impaired sarcoplas- mic reticulum Ca2+ release rate after fatiguing stimulation in rat skeletal muscle. J Appl Physiol 89:210–217 Plaskett CJ, Cafarelli E (2001) CaVeine increases endurance and attenuates force sensation during submaximal isometric con- tractions. J Appl Physiol 91:1535–1544 Rooney KJ, Herbert RD, Balnave RJ (1994) Fatigue contributes to the strength training stimulus. Med Sci Sports Exer 26:1160–1164 Schott J, McCully K, Rutherford OM (1995) The role of metabo- lites in strength training II. Short versus long isometric con- tractions. Eur J Appl Physiol 71:337–341 Schlumberger A, Stec J, Schmidtbleicher D (2001) Single-vs. mul- tiple-set strength training in women. J Strength Cond Res 15:284–289 Stone MH, O’Bryant HS, Schilling BK, Johnson RL, Pierce KC, HaV GG et al (1999) Periodization: eVects of manipulating volume and intensity. Part 1. Strength Cond J 21:56–62 Westcott WL, Winett RA, Anderson ES, Wojcik JR, Loud RL, Cleggett E et al (2001) EVects of regular and slow tempo resistance training on muscle strength. J Sports Med Phys Fit 41:154–158 123
Compartilhar