J Appl Physiol 103: 1565–1575, 2007. First published August 23, 2007; doi:10.1152/japplphysiol.00578.2007. Influence of concentric and eccentric resistance training on architectural adaptation in human quadriceps muscles Anthony J. Blazevich, Dale Cannavan, David R. Coleman, and Sara Horne Centre for Sports Medicine and Human Performance, School of Sport and Education, Brunel University, Uxbridge, United Kingdom Submitted 30 May 2007; accepted in final form 15 August 2007 Blazevich AJ, Cannavan D, Coleman DR, Horne S. Influence of have performed chronic eccentric work (16, 36, 37), whereas concentric and eccentric resistance training on architectural adaptation in decreases (16) or a lack of change (36) is shown in those that human quadriceps muscles. J Appl Physiol 103: 1565–1575, 2007. First worked concentrically. Also, rightward shifts in the force- published August 23, 2007; doi:10.1152/japplphysiol.00578.2007.— length relationship of muscle have been shown after periods of Studies using animal models have been unable to determine the eccentric muscle training (37), which has been suggested to be mechanical stimuli that most influence muscle architectural adapta- attributable to an increase in serial sarcomere number. These tion. We examined the influence of contraction mode on muscle architectural change in humans, while also describing the time course results are strongly indicative of contraction mode being a of its adaptation through training and detraining. Twenty-one men primary stimulus for fiber or fascicle length change, and there and women performed slow-speed (30°/s) concentric-only (Con) or is some acceptance of the proposition that eccentric training eccentric-only (Ecc) isokinetic knee extensor training for 10 wk increases muscle fiber length. Nonetheless, methodological before completing a 3-mo detraining period. Fascicle length of the difficulties involved with clearly establishing the contraction vastus lateralis (VL), measured by ultrasonography, increased simi- mode of the measured muscles [chiefly the rat vastus interme- larly in both groups after 5 wk (⌬Con ϭϩ6.3 Ϯ 3.0%, ⌬Ecc ϭϩ3.1 Ϯ dius (VI)] limit the strength of this evidence (see e.g., Ref. 16). 1.6%, mean ϭϩ4.7 Ϯ 1.7%; P Ͻ 0.05). No further increase was Furthermore, increases in fiber length (or sarcomere number, found at 10 wk, although a small increase (mean ϳ2.5%; not signif- its surrogate when assuming a fixed sarcomere length) have icant) was evident after detraining. Fascicle angle increased in both been reported in muscles that were exercised through large groups at 5 wk (⌬Con ϭϩ11.1 Ϯ 4.0%, ⌬Ecc ϭϩ11.9 Ϯ 5.4%, ϭ Ϯ Ͻ ⌬ ϭϩ Ϯ excursions (34), which is suggestive of muscle excursion range mean 11.5 3.2%; P 0.05) and 10 wk ( Con 13.3 3.0%, (or absolute length) being a primary stimulus. Alternatively, ⌬Ecc ϭϩ21.4 Ϯ 6.9%, mean ϭ 17.9 Ϯ 3.7%; P Ͻ 0.01) in VL only and remained above baseline after detraining (mean ϭ 13.2%); movement velocity has been implicated. In humans, vastus smaller changes in vastus medialis did not reach significance. The lateralis (VL) fascicle length has been shown to be highly similar increase in fascicle length observed between the training predictive of 100-m time in well-trained sprint runners (35), groups mitigates against contraction mode being the predominant and increases in fascicle length were reported both in a group stimulus. Our data are also strongly indicative of 1) a close association of athletes who removed heavy resistance training and in- between VL fascicle length and shifts in the torque-angle relationship creased their high-speed training (9) and in a group of resis- through training and detraining and 2) changes in fascicle angle being tance trainers who performed the concentric phase of their lifts driven by space constraints in the hypertrophying muscle. Thus with maximum velocity (3). Contraction velocity has also been muscle architectural adaptations occur rapidly in response to resis- demonstrated to be an influencing factor in smooth muscle cell tance training but are strongly influenced by factors other than growth (18). Nonetheless, the influence of muscle contraction contraction mode. velocity has yet to be studied in animals, and the elucidation of skeletal muscle; fascicle; muscle adaptation; muscle strength the most significant stimulus for fascicle length adaptation has not been possible with the use of animal models. Thus the possibility remains that a range of mechanical stimuli influence A MUSCLE’S FORCE GENERATING properties are strongly influenced fascicle length. by the architectural arrangement of its fascicles. Therefore, In humans, the measurement of fascicle length in vivo with given that muscle architecture is highly plastic, understanding ultrasonography has revealed marked lengthening in both the mechanical stimuli that influence it is of primary impor- younger (3, 53) and older (47) populations after prolonged tance for those invested in optimizing muscle function and periods of resistance training, and fascicle shortening has been movement performance. In particular, fiber, or fascicle, length reported after gastrocnemius recession in spastic diplegia pa- has a profound effect on muscle excursion range, maximum tients (56). The reliable measurement of fascicle length in shortening velocity (and thus muscle power), and the force- humans offers the opportunity to use human models, which are length relationship. Despite the functional importance of fas- associated with few of the methodological limitations inherent cicle length, the most important mechanical signal required to in animal models. Importantly, contraction mode, muscle ex- stimulate its adaptation has not been identified. cursion, and contraction velocity during a movement can be Examination of the effects of a range of mechanical stimuli easily regulated by using isokinetic dynamometry to system- has typically been performed with animal models. Researchers atically examine the influence of each parameter, and the yet to have reported increases in fiber length in muscles purported to be described temporal response of fascicle length change can Address for reprint requests and other correspondence: A. J. Blazevich, Centre The costs of publication of this article were defrayed in part by the payment for Sports Medicine and Human Performance, School of Sport and Education, of page charges. The article must therefore be hereby marked “advertisement” Brunel Univ., Uxbridge UB8 3PH, UK (e-mail: [email protected]). in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. http://www.jap.org 8750-7587/07 $8.00 Copyright © 2007 the American Physiological Society 1565 1566 MUSCLE ARCHITECTURAL ADAPTATION IN HUMAN QUADRICEPS be examined since repeated measurements are possible with tric-only (Ecc) knee extension training group. The subjects were noninvasive methods. In lieu of the above, the primary purpose tested for strength, muscle size, and muscle architecture at weeks 0, 5, of the present study was to test the hypothesis that fascicle and 10 of the training period and again after 3 mo (14 wk) of length changes are unique to the training contraction mode. detraining. Tests at 5 and 10 wk of training were conducted 4 (muscle The hypothesis would be confirmed if increases in fasci- architecture), 4–5 (strength testing), and 7 (muscle volume; week 10 only) days after the final training session of that training period; tests cle length result from eccentric training but a decrease or no were performed at the same time of day as at week 0. Three subjects change results from concentric training. Given that the time (2 men and 1 woman) withdrew from the training for reasons unre- course of fascicle length change has yet to be described in lated to the study; 10 and 11 subjects completed Con and Ecc training, humans, we measured, for the first time, fascicle length respectively. changes through periods of training (10 wk) and subsequent Resistance training. The subjects performed four (weeks 1–3), five detraining (3 mo). (weeks 4–7), or six (weeks 8–10) sets of six maximal concentric (Con While fascicle length impacts significantly on the length group) or eccentric (Ecc group) knee extension repetitions three times range and speed of active force production, a muscle’s fiber, or a week on an isokinetic dynamometer (Biodex system 3, Biodex fascicle, angle is also of great functional importance. It affects Medical Systems); in the first three sessions the subjects exercised at force production by allowing a greater amount of contractile 50%, 70%, and then 90% of their pretraining maximum to minimize muscle damage resulting from the unaccustomed heavy exercise. At tissue to attach to a given area of tendon or aponeurosis, and by least 1 day separated each session. The Con group trained by extend- increasing the muscle’s architectural gearing ratio (AGR; ratio ing their knee “as fast and hard as possible,” although the dynamom- ε ε of longitudinal muscle strain to fascicle strain, x/ f, during eter lever arm was set to move at 30°/s, from the maximum knee contraction) to allow fascicles the opportunity to produce flexion angle allowed by the dynamometer-seat setup (ϳ100°) to forces at more optimum lengths and shortening speeds (5, 8, maximum knee extension (5–10°) before returning their leg to the 28, 42, 61). Increases in fascicle angle have been reported after start position with a small knee flexion contraction. The Ecc group periods (14–16 wk) of heavy resistance training in humans (1, performed a small knee extension contraction (ϳ20 Nm) to move the 30), although studies of shorter duration have been unable to leg to an extended (10–15°) position before maximally extending the agree on its temporal response (10, 53). It is also not clear how knee to resist the subsequent downward movement of the lever arm of different muscles within a synergistic group respond to the the dynamometer. The subjects were asked to “stop the dynamometer” by applying a maximum upward force, although the dynamometer same stimulus.