Eur J Appl Physiol (1998) 77: 170±175 Ó Springer-Verlag 1998

ORIGINAL ARTICLE

Philip D. Chilibeck á Aaron W. Calder á Digby G. Sale Colin E. Webber A comparison of strength and muscle mass increases during resistance training in young women

Accepted: 8 July 1997

Abstract Strength gains with resistance training are due strength were accompanied by muscle hypertrophy and, to muscle hypertrophy and nervous system adaptations. presumably, a faster neural adaptation. The contribution of either factor may be related to the Key words Strength á Females á Hypertrophy á Neural complexity of the exercise task used during training. The adaptation purpose of this investigation was to measure the degree to which muscle hypertrophy contributes to gains in strength during exercises of varying complexity. Nine- teen young women resistance trained twice a week for 20 Introduction weeks, performing exercises designed to provide whole- body training. It is well known that the strength of a muscle is pro- The lean mass of the trunk, legs and arms was mea- portional to its cross-sectional area (CSA; Sale et al. sured by dual energy x-ray absorptiometry and com- 1987). However, many resistance training studies have pared to strength gains (measured as the 1-repetition shown poor relationships between gains in strength and maximum) in bench press, leg press and arm curl exer- muscle hypertrophy. Rapid, early gains in strength are cises, pre-, mid- (10 weeks) and post-training. No often accompanied by little or no hypertrophy (Wilmore changes were found in a control group of ten women. 1974; Jones and Rutherford 1987; Cureton et al. 1988; For the exercise group, increases in bench press, leg Davies et al. 1988, Narici et al. 1989; Staron et al. 1989; press and arm curl strength were signi®cant from pre- to Ishida et al. 1990). Early gains in strength may be due to mid-, and from mid- to post-training (P < 0.05). In adaptations within the nervous system such as increased contrast, increases in the lean mass of the body segments motor neurone activation and motor unit synchroniza- used in these exercises followed a di€erent pattern. In- tion (Sale 1988). creases in the lean mass of the arms were signi®cant Various measurement techniques have been em- from pre- to mid-training, while increases in the lean ployed to provide evidence that motor neurone activa- mass of the trunk and legs were delayed and signi®cant tion is increased with resistance training. This evidence from mid- to post-training only (P < 0.05). It is con- includes increases in integrated electromyographic ac- cluded that a more prolonged neural adaptation related tivity (EMG. Moritani and deVries 1979; HaÈ kkinen and to the more complex bench and leg press movements Komi 1983; HaÈ ikinen et al. 1985; Higbie et al. 1996), may have delayed hypertrophy in the trunk and legs. re¯ex potentiation (Sale et al. 1983a, 1983b) and maxi- With the simpler arm curl exercise, early gains in mal voluntary contraction (MVC) to maximal twitch torque ratio (Ishida et al. 1990). Motor unit synchroni- zation has also been shown to be enhanced with resis- tance training, as measured by EMG (Milner-Brown P.D. Chilibeck á A.W. Calder á D.G. Sale et al. 1975). These neural adaptations appear to occur Department of Kinesiology, McMaster University, before muscle hypertrophy and may be necessary before Hamilton, Ontario, Canada, L8S 4K1 hypertrophy is seen with resistance training (Sale 1988). C.E. Webber Complex resistance exercises, such as those involving Department of Nuclear Medicine, McMaster University, Hamilton, Ontario, Canada, L8S 4K1 movement at more than one joint (i.e. the bench press or leg press), may involve a longer initial neural adaptation P.D. Chilibeck (&) College of Physical Education, compared with simpler single-joint exercises, and this University of Saskatchewan, Saskatoon, may result in delayed hypertrophy. Rutherford and Saskatchewan, Canada, S7N 5C2 Jones (1986) showed that with increasing complexity of 171 exercise, learning and co-ordination become the main exercise was increased when the upper limit of the prescribed rep- factors contributing to gains in weight lifting perfor- etition range could be achieved with good exercise ``form''. Strength in the bench press, arm curl and leg press exercises was mance. This suggests that muscle hypertrophy plays a measured as the 1 RM; that is, the heaviest weight that could be small role during the early enhancement of weight lifting lifted only once. A standard protocol was used (Sale 1991). performance during complex exercises. The lean tissue mass of the arm, leg and trunk subregions, In analysing the results of a study designed to ex- corresponding to body segments that are dominant during the arm curl, leg press and bench press, respectively, was measured with the amine the e€ects of weight training on bone mass in aid of whole-body scans obtained by dual-energy X-ray young women (Chilibeck et al. 1996), and the relative absorptiometry (DEXA) on a Hologic 1000 W DPX densitometer e€ectiveness of whole- versus split-body weight training (Waltham, Massachusetts 02154, USA). To obtain this measure- routines (Calder et al. 1994), we observed a striking ment, the subjects lay in a supine position within speci®c markings di€erence in the pattern of increases in strength and lean upon the scan table and beside a soft tissue standard, while the densitometer scanned from head to toe. Analysis of the original mass in response to training exercises representing scans involved the de®ning of speci®c subregions of the body by the complex (multi-joint) versus simple (single-joint) move- operator. A ``compare'' feature, incorporated into the Hologic ments. Speci®cally, the present report compares the hy- software (version 5.56), allows analysis of duplicate scans by pertrophy and strength adaptations to bench press and comparison to the original scan made on a subject. This provides for the identical placement of regions of interest between two scans, leg press exercises, representing complex exercises, and making duplicate scans more reproducible. All scans were per- the elbow ¯exion curl exercise, representing simple ex- formed and analysed by the same technician. The precision (re- ercises. It was found that hypertrophy was delayed in the producibility) of lean tissue measurements by the DEXA machine musculature serving the complex exercises. It is sug- used in the present study was determined previously in a group of gested that the delayed hypertrophy response is the re- 21 young women (Chilibeck et al. 1994). The coecients of varia- tion (CVs) for subregions were 2.0%, 2.0% and 5.7% for the trunk, sult of a longer neural adaptation phase necessitated by legs and arms, respectively. the complexity of the training exercises. All measurements on the training group were performed pre-, mid- (after 10 weeks) and post-training, while measurements on the control group were performed only pre- and post-training. Pre- and post-training data were analysed by a two factor Methods (group ´ time) analysis of variance (ANOVA) with repeated measures on one factor (time, pre/post). Pre-, mid- and post- Twenty-nine young women with minimal strength training experi- training measures for the training group were analysed using a ence served as subjects. Nineteen women were assigned to a repeated measures ANOVA. Tukey post-hoc tests determined training group and the remaining ten comprised a control group. signi®cant di€erences among mean values. Signi®cance was ac- The groups did not di€er signi®cantly in age, height, body mass or cepted at P<0.05. physical activity patterns. The mean (SD) age, height and body mass of the training group were 20.2 (0.8) years, 166.2 (5.4) cm and 60.8 (7.0) kg respectively. The corresponding values for the control group were 20.2 (0.4) years, 165.8 (6.5) cm and 61.9 (7.7) kg res- Results pectively. Subjects were fully informed of the procedures and signed a consent form before the start of the study, which carried the approval of the McMaster University Ethics Committee. For the training group, strength (1 RM) increased sig- Resistance training exercises were performed twice a week for ni®cantly throughout the entire program, from pre- to 20 weeks. Subjects performed the complex (de®ned as movement at mid- (10 weeks) training and from mid- to post- (20 more than one joint) exercises of the bench press (transverse weeks) training, for the arm curl (Fig. 1a), bench press shoulder ¯exion, combined with elbow extension) and leg press (combined hip and knee extension), and the simple (de®ned as (Fig. 2a), and leg press (Fig. 3a) exercises. Unlike movement at one joint) exercise of the arm ``curl'' (elbow ¯exion). strength, the lean mass of the body segments increased All exercises were performed bilaterally. Two additional upper only during speci®c time points. Gains in lean mass body exercises, the ``lat'' pulldown (shoulder adduction and elbow during the ®rst 10 weeks of training were signi®cant in ¯exion) and triceps (elbow) extension, and two additional lower body exercises of knee extension and knee ¯exion were also in- the arms only (Fig. 1b). Gains in trunk and legs lean cluded to ensure overall muscle balance. The upper body exercises mass were signi®cant from mid- to post-training (Figs. were performed for ®ve sets of 6±10 repetitions maximum (RM), 2b and 3b), while mid- to post-training gains in arms lean while the lower body exercises were performed for ®ve sets of 10±12 mass were smaller and not signi®cant (Fig. 1b). Percent RM. The greater number of repetitions prescribed for the lower changes in strength and lean mass measures are shown in body exercises took into account our previous observations that for a given percentage of the 1 RM, more repetitions can be performed Table 1. With the precision (CVs) of the DEXA mea- with lower body than with upper body exercises (Sale and Mac- surements, our sample size of 19 in the training group Dougall 1981; Sale et al. 1990b). Based on these observations, we was adequate to demonstrate the above treatment e€ects estimated that training weights equivalent to 75±90% 1 RM would with an a level of 0.05 and a power of 0.9 (Chilibeck et al. result in sets of 6±10 RM in upper body exercises and 10±12 RM in lower body exercises. Ten of the exercise-trained subjects per- 1994). In general, gains in lean mass correlated poorly formed all exercises on the same day, resulting in 2 training days with gains in strength. Signi®cant correlations were per week, while nine of the exercise-trained subjects performed a found for gains in legs lean mass versus gains in leg press ``split'' routine, such that upper body exercises were performed on strength mid- to post-training (r = 0.51, P < 0.05) and Monday and Thursday and lower body exercises on Tuesday and Friday of each week. A comparison of the ``whole-'' versus ``split- gains in trunk lean mass versus gains in bench press body'' routines was the subject of a separate study (Calder et al. strength pre- to post-training (r = 0.50, P < 0.05). 1994). Each exercise session was supervised and the resistance, sets, There were no signi®cant changes for any lean mass or and repetitions entered into training logs. The resistance used in an strength measures in the control group. 172

Fig. 1 A Changes in arm curl strength, and B arms lean mass throughout 20 weeks of training. Error bars indicate standard deviations. (1RM1-Repetition maximum, pre pre-training, mid Fig. 2 A Changes in bench press strength, and B trunk lean mass mid-training, post post-training). * Signi®cantly di€erent from pre- throughout 20 weeks of training. Error bars indicate standard training value (P < 0.05); ** signi®cantly di€erent from mid-training deviations. * Signi®cantly di€erent from pre-training value (P < value (P < 0.05) 0.05); ** signi®cantly di€erent from mid-training value (P < 0.05)

prime movers may have to increase in strength or im- Discussion prove their ability to activate and co-ordinate contrac- tions. This results in strength improvements before It has been suggested that adaptations within the ner- signi®cant hypertrophy of the prime movers occurs vous system, rather than muscle hypertrophy, account (Rutherford and Jones 1986). This is consistent with the for increases in strength during the ®rst few weeks of present results where hypertrophy appeared to be de- resistance training (Sale 1988). In the present study, this layed in the trunk and leg regions while bench and leg seems to be true with regard to the bench and leg press press strength increased early. exercises; since the majority of strength gains were ac- A review of training studies using either simple single- complished during the ®rst half (10 weeks) of the joint or complex multi-joint exercises, outlined below, training period, without signi®cant hypertrophy, as es- supports our ®nding that muscle hypertrophy occurs timated by changes in lean mass of the trunk and legs. In earlier when simpler exercises are performed. contrast, with the arm curl exercise, gains in lean mass of In females who trained with simple single-joint exer- the arms occurred relatively early, with signi®cant cises, hypertrophy occurred early whether leg or upper changes occurring only during the ®rst half of the body exercises were performed. Quadriceps CSA, as training program. measured by ultrasound (Young et al. 1983) or magnetic The di€erences between the leg and bench press ver- resonance imaging (MRI; Higbie et al. 1996) increased sus the arm curl exercise with respect to the pattern of by 5.0±6.6% following 5±10 weeks of unilateral knee changes in lean mass may be related to their level of extension training, and upper arm CSA, as measured by complexity. Rutherford and Jones (1986) suggested that computerized tomography (CT), increased by 5.4±7.9% with a more complex exercise, learning and coordination following 6±16 weeks of elbow ¯exor or extensor train- play a dominant role early in training. This may delay ing (Cureton et al. 1988; Davies et al. 1988). Similar hypertrophy of the muscle groups used in these exer- degrees of early hypertrophy have been observed in cises. They state that with complex exercises (such as the males following training with single-joint exercises: leg and bench press) that involve movement at more Quadriceps CSA, as measured by MRI (Narici et al. than one joint, ®xator muscles used in support of the 1989) or CT (Jones and Rutherford 1987), increased by 173 resulted in signi®cant gains in strength, but little hy- pertrophy after 7±16 weeks of training when quadriceps CSA was measured by ultrasound (Dons et al. 1979) or CT (Cureton et al. 1988; Brown et al. 1990), or when muscle ®bre size was measured from biopsy samples (HaÈ kkinen and Komi 1983). Thus, it seems that muscle hypertrophy is delayed when complex exercises are used for training. This may be due to a more prolonged neural adaptation compared to simpler exercises. Similar to our ®ndings, most of the above training studies have demonstrated poor correlations between muscle mass and strength gains, even for simpler exer- cises. This suggests that neural mechanisms always play a role in strength gains early in training. A longer neural adaptation when training with complex exercises may involve several aspects of the nervous system. Changes in maximal muscle activation levels with training may occur at di€erent rates with complex versus simple exercises. During simple exercis- es, motor unit activation, as determined by the inter- polated-twitch technique, is close to 100% in the untrained state (Vandervoort and McComas 1986; Brown et al. 1990; Sale et al. 1992) and changes little with training (Brown et al. 1990; Sale et al. 1992). De- termination of motor unit activation during complex exercises would be technically dicult, but it is possible that when compared to simple exercises, activation is not Fig. 3 A Changes in leg press strength, and B legs lean mass as complete and an increase in this parameter would throughout 20 weeks of training. Error bars indicate standard require longer training periods. Longer training periods deviations. * Signi®cantly di€erent from pre-training value (P < for full activation may be required because of higher 0.05); ** signi®cantly di€erent from mid-training value (P < 0.05) motor unit numbers and innervation ratios (muscle ®- bres per motor unit) in the muscle groups involved in complex exercises. The muscle groups used in the com- 5±8.5% following 9±12 weeks of unilateral knee ¯exion plex leg press exercise (vastus lateralis and gastro- training, and upper arm CSA, as measured by CT cnemius) have a larger number of motor units and a (Cureton et al. 1988; Brown et al. 1990) or MRI (McCall higher innervation ratio compared to those used in the et al. 1996), increased 7.9±17.4% following 12±16 weeks simple arm curl exercise (biceps brachii, Feinstein et al. of elbow ¯exion or extension training. 1955; Galea et al. 1991). To our knowledge there are no In contrast to the above training studies employing data on the muscle groups used in the bench press ex- simpler exercises, training programs using complex ex- ercise. If training with complex exercises involves a ercises have resulted in little or no muscle hypertrophy longer period before full neural activation is realized, early in training. Females who trained using the mainly then any e€ects that neurotrophic factors may have on multi-joint exercises of squats and leg press had signi®- muscle characteristics (i.e. hypertrophy, Markelonis and cant changes in lower extremity strength by 8±16 weeks, Oh 1979; Thesle€ et al. 1990) may be delayed. The re- but no change in thigh girth or CSA (Cureton et al. sults of the present study only allow speculation on the 1988; Staron et al. 1989). Studies of males who trained possible causes of delayed hypertrophy when training using mainly squat or leg press exercises have, similarly, with complex exercises. Further research is required

Table 1 Percent increases in strength and lean mass mea- Pre- to mid-training Mid- to post-training sures with training (0±10 weeks) (10±20 weeks)

Arm curl strength 50.5%* 15.0%* Arms lean mass 7.5%* 2.3% Bench press strength 22.3%* 8.4%* Trunk lean mass 0.5% 2.7%* Leg press strength 12.6%* 7.5%* Legs lean mass 1.4% 2.0%*

* Percent increase is signi®cant (P<0.05) 174 before conclusions can be drawn as to the characteristics the short duration of training (20 weeks) used in the of neural adaptations and their e€ect on rates of muscle present study, however, the use of female subjects might hypertrophy with di€erent exercise training regimens. not have had a limiting e€ect on the amount of hyper- One limitation to the present study was the use of trophy possible. In a recent study we demonstrated that other exercises that trained the same musculature as the the absolute hypertrophy that occurs in response to a bench press, leg press and arm curl. These additional training program of this duration is similar in female exercises were used in a study of the e€ects of whole- and male individuals (O'Hagan et al. 1995). Longer versus split-body weight training routines (Calder et al. durations of strength training may be necessary before 1994). The ``lat'' pulldown exercise involves the elbow sex di€erences, with respect to hypertrophy, are ob- ¯exors and the sternal portion of the pectoralis major, so served. Therefore, the use of female, as opposed to male it involves muscles used in both the arm curl and bench subjects, in the short-duration program of the present press. Its inclusion, therefore, is likely to have had a study, may not have a€ected the amount of hypertrophy similar e€ect on both the arm curl and bench press ex- observed. ercises, minimally e€ecting the comparison between A second factor that may have limited the amount of these two exercises. The addition of knee extension and hypertrophy possible was the training volume used. It is knee ¯exion exercises may have had an e€ect on the recognized that resistance training programs, with ex- musculature trained by the leg press exercise. It could be ercises performed three to four times per week (as op- argued that the leg press involves the musculature both posed to the twice per week training of the present above and below the knee, which was measured as the study), are optimal for producing muscle hypertrophy. total leg lean tissue mass in the present study, whereas However, we have shown previously that the training the knee curl and extension involved only the muscula- volume used in the present study produces a substantial ture above the knee. If the knee extension and curl ex- muscle hypertrophy (Sale et al. 1990a). This training ercises did have a substantial e€ect on the total leg lean volume therefore seems to be adequate for studying the tissue measures, this indicates that even with simple ex- rates of muscle hypertrophy that occur with strength ercises, hypertrophy is more dicult to achieve in leg training. versus upper body muscles. This is consistent with data In summary, our results indicate that training with showing that bodybuilders and powerlifters exceed un- complex exercises (bench and leg press) causes delayed trained subjects to a greater extent in upper rather than muscle hypertrophy when compared to a less complex lower limb strength and muscle size (Sale and Mac- exercise (arm curl). This may be due to a prolonged Dougall 1984). The lesser responsiveness of the legs to neural adaptation when training with complex exercises. training may re¯ect their greater initial state of training because of their role in posture and locomotion. Acknowledgements Chris Gordon, John Moroz, and Douglas It could be argued that our strength measures of 1 Oleksuik provided technical assistance. The study was supported by Sport Canada and the Natural Sciences and Engineering Re- RM do not represent real strength measures such as search Council of Canada. those obtained isometrically or isokinetically. However, this measure is justi®ed in that increases in strength are not only speci®c to the muscles involved in training, but also to the movement patterns used during training (Sale References and MacDougall 1981). We have shown previously that Brown AB, McCartney N, Sale DG (1990) Positive adaptations to muscle hypertrophy occurs in response to weight train- weight-lifting training in the elderly. J Appl Physiol 69:1725± ing with no corresponding increases in isometric MVC 1733 or twitch torque (Sale et al. 1992). Others have also Calder AW, Chilibeck PD, Webber CE, Sale DG (1994) Com- shown that muscle hypertrophy occurs without in- parison of whole and split weight training routines in young women. Can J Appl Physiol 19:185±199 creased strength when measured in a type of muscle Chilibeck P, Calder A, Sale DG, Webber C (1994) Reproducibility action not used in training (Higbie et al. 1996). These of dual-energy x-ray absorptiometry. Can Assoc Radiol J speci®c training responses add further to the neural 45:297±302 hypothesis of training adaptations with respect to Chilibeck PD, Sale DG, Webber CE (1995) Exercise and bone movement patterns. mineral density. Sports Med 19:103±122 Chilibeck PD, Calder A, Sale DG, Webber CE (1996) Twenty If we had used male subjects (as opposed to the fe- weeks of weight training increases lean tissue mass but not bone males used in the present study) with a greater potential mineral mass or density in healthy, active young women. Can J for hypertrophy, di€erent patterns of muscle mass gains Physiol Pharmacol 74:1180±1185 in response to a similar weight training program may Cureton KJ, Collins MA, Hill DW, McElhannon FM (1988) Muscle hypertrophy in men and women. Med Sci Sports Exerc have been observed. A female population was used in 20:338±344 the present study because, in addition to muscle mass Davies J, Parker DF, Rutherford OM, Jones DA (1988) Changes in measures, we were interested in determining the e€ec- strength and cross sectional area of the elbow ¯exors as a result tiveness of the weight training program on bone mass of isometric strength training. Eur J Appl Physiol 57:667±670 Dons B, Booerup K, Cone-Petersen F, Hancke S (1979) The e€ect (Chilibeck et al. 1996), as this has been recommended as of weight-lifting exercise related to muscle ®bre composition a measure protecting against the development of osteo- and muscle cross-section area in humans. Eur J Appl Physiol porosis in this population (Chilibeck et al. 1995). With 40:95±106 175

Feinstein B, LindegaÊ rd B, Nyman E, Wohlfart G (1955) Mor- Sale DG (1988) Neural adaptation to resistance training. Med Sci phologic studies of motor units in normal human muscles. Acta Sports Exerc Suppl 20:S135±S145 Anat (Basel) 23:127±142 Sale DG (1991) Testing strength and power. In: MacDougall JD, Galea V, De Bruin H, Cavasin R, McComas AJ (1991) The Wenger HA, Green HJ (eds) Physiological testing of the elite numbers and relative sizes of motor units estimated by com- athlete. Human Kinetics, Champaign, Illinois pp 21±106 puter. Muscle Nerve 14:1123±1130 Sale DG, MacDougall D (1981) Speci®city in strength training: a HaÈ kkinen K, Komi P (1983) Electromyographic changes during review for the coach and athlete. Can J Appl Sports Sci 6:87±92 strength training and detraining. Med Sci Sports Exerc 15:455± Sale DG, MacDougall JD (1984) Isokinetic strength in weight- 460 trainers. Eur J Appl Physiol 53:128±132 HaÈ kkinen K, Allen M, Komi PV (1985) Changes in isometric force- Sale DG, Upton ARM, McComas AJ, MacDougall JD (1983a) and relaxation-time, electromyographic and muscle ®bre char- Neuromuscular function in weight-trainers. Exp Neurol acteristics of human skeletal muscle during strength training 82:521±531 and detraining. Acta Physiol Scand 125:573±585 Sale DG, MacDougall JD, Upton ARM, McComas AJ (1983b) Higbie EJ, Cureton KJ, Warren GL, Prior BM (1996) E€ects of E€ect of strength training upon motoneuron excitability in concentric and eccentric training on muscle strength, cross- man. Med Sci Sports Exerc 15:57±62 sectional area, and neural activation. J Appl Physiol 81:2173± Sale DG, MacDougall JD, Alway SE, Sutton JR (1987) Voluntary 2181 strength and muscle characteristics in untrained men and Ishida K, Moritani T, Itoh K (1990) Changes in voluntary and women and bodybuilders. J Appl Physiol 62:1786±1793 electrically induced contractions during strength training and Sale DG, Jacobs I, MacDougall JD, Garner S (1990a) Comparison detraining. Eur J Appl Physiol 60:244±248 of two regimens of concurrent strength and endurance training. Jones DA, Rutherford OM (1987) Human muscle strength train- Med Sci Sports Exerc 22:348±356 ing: the e€ects of three di€erent regimes and the nature of the Sale DG, MacDougall JD, Jacobs I, Garner SH (1990b) Interac- resultant changes. J Physiol (Lond) 391:1±11 tion between concurrent strength and endurance training. Markelonis GJ, Oh TH (1979) A sciatic nerve protein has a trophic J Appl Physiol 68:260±270 e€ect on development and maintenance of skeletal muscle cells Sale DG, Martin JE, Moroz DE (1992) Hypertrophy without in- in culture. Proc Natl Acad Sci 76:2470±2474 creased isometric strength after weight training. Eur J Appl McCall GE, Byrnes WC, Dickinson A, Pattany PM, Fleck SJ Physiol 64:51±55 (1996) Muscle ®bre hypertrophy, hyperplasia, and capillary Staron RS, Malicky ES, Leonardi MJ, Falkel JE, Hagerman FC, density in college men after resistance training. J Appl Physiol Dudley GA (1989) Muscle hypertrophy and fast ®bre type 81:2004±2012 conversions in heavy resistance-trained women. Eur J Appl Milner-Brown HS, Stein RB, Lee RG (1975) Synchronization of Physiol 60:71±79 human motor units: possible roles of exercise and supraspinal Thesle€ S, Molgo J, TaÊ gerud S (1990) Trophic interrelations at the re¯exes. Electroencephalog Clin Neurophysiol 38:245±254 neuromuscular junction as revealed by the use of botulinum Moritani T, DeVries HA (1979) Neural factors versus hypertrophy neurotoxins. J Physiol (Paris) 84:167±173 in the time course of muscle strength gain. Am J Phys Med Vandervoort AA, McComas AJ (1986) Contractile changes in 58:115±130 opposing muscles of the human ankle joint with aging. J Appl Narici MV, Roi GS, Landoni L, Minetti AE, Cerretelli P (1989) Physiol 61:361±367 Changes in force, cross-sectional area and neural activation Wilmore JH (1974) Alterations in strength, body composition and during strength training and detraining of the human quadri- anthropometric measurements consequent to a 10-week weight ceps. Eur J Appl Physiol 59:310±319 training program. Med Sci Sports Exerc 6:133±138 O'Hagan FT, Sale DG, MacDougall JD, Garner SH (1995) Re- Young A, Stokes M, Round JM, Edwards RHT (1983) The e€ect sponses to resistance training in young women and men. Int J of high-resistance training on the strength and cross-sectional Sports Med 16:314±321 area of the human quadriceps. Eur J Clin Invest 13:411±413 Rutherford OM, Jones DA (1986) The role of learning and coor- dination in strength training. Eur J Appl Physiol 55:100±105