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Impact of Acceleration on Blood Lactate Values Derived From High-Speed Resistance Exercise

Caruso, John F1; Hari, P2; Leeper, Adam E2; Coday, Michael A1; Monda, Julie K1; Ramey, Elizabeth S1; Hastings, Lori P1; Golden, Mallory R1; Davison, Steve W1

Journal of Strength and Conditioning Research: October 2009 - Volume 23 - Issue 7 - p 2009-2014
doi: 10.1519/JSC.0b013e3181b3dce7
Original Research

Caruso, JF, Hari, P, Leeper, AE, Coday, MA, Monda, JK, Ramey, ES, Hastings, LP, Golden, MR, and Davison, SW. Impact of acceleration on blood lactate values derived from high-speed resistance exercise. J. Strength Cond Res 23(7): 2009-2014, 2009-Acceleration, or an increase in the rate of movement, is integral to success in many sports. Improvements in acceleration often entail workouts done at intensities that elicit higher blood lactate concentrations (BLa). The purpose of the study is to assess the impact of acceleration on BLa. Methods required subjects (n = 45) to perform 4 workouts that each involved two 1-minute sets of hip- and knee-extension repetitions on an inertial exercise trainer (Impulse Training Systems, Newnan, Georgia). Subjects performed 2 workouts comprised solely of phasic or tonic repetitions; their sequence was randomized to prevent an order effect. Before and 5 minutes after exercise, subjects' BLa were assessed with a calibrated analyzer (Sports Resource Group, Hawthorne, New York). Post and delta (post-pre) BLa both served as criterion measures for multivariate analysis. Average and peak acceleration values, derived from both phasic and tonic workouts, served as predictor variables. Results showed statistical significance (p < 0.05; R 2 = 0.2534) and yielded the following prediction equation from phasic workouts: delta BLa = 1.40 + 1.116 (average acceleration set 1) - 0.011 (peak acceleration set 1) - 0.634 (average acceleration set 2) + 0.005 (peak acceleration set 2). Conclusions suggest delta BLa variance, which represents the increase of the metabolite incurred from workouts, is most easily explained by average acceleration values, which describes the mean increase in the rate of movement from phasic workouts. To improve an athlete's tolerance for acceleration-induced BLa increases, workouts should be tailored with respect to the muscles involved and the duration of exercise bouts of their chosen sport.

1Exercise and Sport Sciences Program, The University of Tulsa, Tulsa, Oklahoma; and 2Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, Oklahoma

Address correspondence to John F. Caruso, john-caruso@utulsa.edu.

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Introduction

Conditioning programs for athletes routinely include resistive exercise (RE) workouts to improve performance. Adaptations to such programs may include greater tolerance of metabolic acidosis and its byproducts, such as higher blood lactate concentrations (BLa). Traditional RE workouts done on standard equipment (barbells, dumbbells, etc.) note variables such as the load imposed, volume of work performed, and the duration of rest periods account for much of the variance in BLa (5-7,11,14,16,26), yet for many sports (e.g., track and field, soccer, rugby, baseball, basketball) the speed of movement attained with actual competition far exceeds those for traditional RE repetitions (9,10,22,23,28). Given the differences in rates of movement attained, variables must be identified that explain more of the BLa variance acquired through the aforementioned high-velocity sports. Furthermore, conditioning programs for improved modern-day athletic performance should include RE devices that better simulate movement rates achieved with actual competition. Variables measured from such high-speed RE thus may serve as better predictors of BLa variance attained with many competitive sports.

Increases in the rate of movement, such as those achieved during athletic competition, are termed acceleration. Faster rates of movement heighten cellular reliance on anaerobic glycolysis, which yield higher BLa and greater fatigue that in turn impair an athlete's ability to accelerate (2,29). Acceleration has received little attention from RE workouts aimed at athletic conditioning because the equipment and paradigms (heavy loads lifted in a slow fashion) used enable little acceleration. Better suited for athletic competition are workouts that improve tolerance for metabolic acidosis done on high-speed RE equipment. One such device, often used for rehabilitative purposes, permits repetitions to occur at high rates of acceleration. Named an inertial exercise trainer (IET; Impulse Training Systems, Newnan, Georgia), workouts entail forced exertion against a small mass from a weight sled that traverses a low-friction track (8). Unlike standard RE equipment, the Iet allows execution of high-speed repetitions to provide more sport-specific adaptations and to best simulate acceleration generated during athletic competition.

Conditioning programs to improve an athlete's acceleration have begun to incorporate IET workouts in a manner that enables them to tolerate increased metabolic acidosis and higher exercise intensities (12,15). IET overhead and side-view illustrations appear in Figures 1 and 2, respectively. Sled resistance is imposed with a Velcro strap and nylon cord intertwined through a series of pulleys (Figure 2). Two types of repetitions may be done on the IET. Termed tonic and phasic repetitions, the former entails continual application of low-level resistance over a full range of motion, which occurs as the cord is kept continuously taut (8). In contrast, phasic repetitions involve oscillatory actions, whereby the cord alternately becomes slack and taut over a single muscle action to impose none or all of the weight sled load (8). Differences in the way repetitions are done may evoke stark contrasts in acceleration and BLa and dictate the merits of IET conditioning programs for athletes.

Figure 1

Figure 1

Figure 2

Figure 2

Because BLa affects improvements to training and competition, and higher rates of movement dictate success in many sports, our study's purpose is to examine acceleration as a BLa predictor from IET workouts. We hypothesize acceleration will account for a significant degree of BLa variance incurred from RE. We also hypothesize, because of the way repetitions are performed, phasic actions will elicit higher acceleration values (30). Results may benefit exercise prescription for those who seek improved tolerance for metabolic acidosis and BLa acquired through increases in their rate of movement.

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Methods

Experimental Approach to the Problem

To assess how well acceleration predicts BLa variance, subjects (n = 45) performed 4 workouts, each comprised solely of phasic or tonic repetitions, on an instrumented IET. Subjects performed 2 phasic and tonic workouts each, their sequence randomized to prevent an order effect. Each workout examined BLa that resulted from seated knee- and hip-extension RE done with subjects' left legs. The workout protocol entailed two 1-minute sets separated by a 90-second rest period. Both average and peak acceleration values were collected from each set, which served as current study predictor variables. Both before and 5 minutes after the conclusion of workouts, subjects submitted to finger pricks to assess post and delta (post-pre) BLa, which served as the 2 current criterion variables. Thus, our experimental approach shows how acceleration may predict the BLa variance and enables us to test each of our hypotheses.

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Subjects

Healthy college-age volunteers (32 women, 13 men) gave written informed consent for the project, which received Institutional Review Board approval from a university-based human subjects committee. General subject characteristics (mean ± SEM) were as follows: height 1.73 ± 0.01 m, weight 74.5 ± 2.5 kg, and body mass index 24.6 ± 0.5 kg m−2. Each subject made 6 visits to our laboratory spaced at least 48 hours apart. Per subject, all 6 visits occurred within a 30-day period. Our data collection timetable accommodated for the daily schedules of our volunteers (classes, work, etc.) such that laboratory visits per subject were made at the same time of day.

Current subjects averaged 2 years prior RE experience, yet none had performed IET workouts. Thus, each subject's first 2 laboratory visits were familiarization sessions, whereby they were introduced to RE on the IET. Preceded by a 5-minute stationary cycle ergometer warm-up performed against 9.8N of resistance at a self-selected velocity, familiarization sessions developed motor patterns specific to tonic and phasic actions. Once familiarization sessions were completed, the final 4 laboratory visits entailed 2 tonic and phasic workouts each, with their sequence randomized to prevent an order effect. Each workout was comprised solely of 1 type of repetition. The current study RE, which enabled performance of both tonic and phasic repetitions, was a seated hip- and knee-extension maneuver with the left leg. A unilateral maneuver was chosen in lieu of the difficulty of a similar RE done in a bilateral fashion on the IET. The RE chosen involves the largest muscles of the body and those responsible for acceleration in numerous high-velocity sports and greater BLa.

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Workouts

At the start of workouts subjects were first weighed and then provided a drop of whole blood to determine their pre-RE BLa. The blood drop was obtained via a finger prick under aseptic conditions. Blood sample analyses were done with a calibrated device (Accutrend Sports Resource Group, Hawthorne, New York) that demonstrates a high degree of data reliability (3). After pre-RE BLa, subjects performed a warm-up identical to that used for familiarization sessions. During warm-ups subjects were randomized to a tonic or phasic workout. For tonic repetitions resistance was incurred through a full range of motion because the cord that connects subject to the weight sled was kept continuously taut. In contrast, phasic actions involved a cyclic pattern to cord movement in which it both slackened and tightened over the course of each repetition, which allowed intermittent application of the weight sled load. Subjects performed the RE seated in a chair that faced the opening of the U-shaped IET (Figure 1). Chair position was held constant per subject. Workouts entailed two 1-minute sets separated by a 90-second rest period. With 8.1 kg added to the sled and a Velcro strap wrapped around the distal portion of their left foot, subjects performed as many repetitions as possible per set. Subjects were told to move the sled as rapidly as possible, not to pace themselves, and received vocal encouragement. After completion of the second set, subjects remained seated. At 5 minutes post-RE BLa was again measured with the same methods used at the start of workouts.

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IET Instrumentation

Per set, peak and average acceleration values were calculated from data collected online. Peak accelerations were the highest increase in the rate of movement observed from a single repetition from each 1-minute set. Per repetition, acceleration was measured from the start of each movement until attainment of a peak velocity. In contrast, average accelerations were the mean rate of movement increase per set. To derive peak and average acceleration values, IET instrumentation required continuous calculation of weight sled position and force output throughout sets. Whereas the current RE was a unilateral maneuver, IET right and left halves (Figure 1) were instrumented in an identical manner. Each half was equipped with a TLL-2K load cell (Transducer Techniques, Temecula, California) attached to its lowest pulley and an infrared position sensor (model CX3-AP-1A, Automationdirect.com) located midway on the underside of each 1.9-m track. As the sled traversed the track, the load cell and position sensor concurrently recorded force output and displacement, respectively. DI-158U signal conditioners (DATAQ Instruments, Akron, Ohio) received load cell and position sensor data measured by a 4-channel analog data acquisition card at 4,000 Hz. Instrumentation included a power source (Model Dual 0-30VDC/3A & 5VDC/3A; Jones & Associates, Lake Park, Florida). A macro was written to perform the numerical integration of force data and was calculated on an Excel spreadsheet. Per repetition, acceleration was calculated as the force:mass ratio.

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Statistical Analyses

Per workout mode (phasic, tonic), pre, post and delta RE BLa were initially assessed for data reproducibility with intraclass correlation coefficients (ICC). Average and peak acceleration values, collected from each phasic and tonic workout set, were assessed for both intraworkout (set 1 vs. set 2) and interworkout (set 1 workout 1 vs. set 1 workout 2, etc.) data reproducibility with ICC. High average and peak acceleration ICC values were then pooled for multivariate regression. Both post-RE and delta BLa served as criterion variables. Per workout mode, multivariate regression included 4 predictor variables-namely, average and peak acceleration values from each of the 2 workout sets. An α ≤ 0.05 determined statistical significance for the multivariate regression analyses.

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Results

BLa ICC values (Table 1) reveal a higher data reproducibility post-RE, likely because the current RE treatment led subjects to become more similar with respect to BLa. Pre-RE BLa were not used in multivariate regression. Intraworkout and interworkout acceleration ICC values appear in Tables 2 and 3, respectively. Prior RE studies (18,19), in which workouts were done over a single plane of motion and far fewer repetitions, claim ICC values of 0.75 to 0.80 indicate excellent reproducibility. Given IET repetitions permit multiplanar and joint movement at high speeds, current acceleration data appear to be reproducible. Acceleration data thus were pooled from the 2 phasic and tonic workouts for use as predictor variables in multivariate regression.

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Criterion and predictor raw data appear in Table 4. Differences in gender sample size led male and female data to be pooled for multivariate regression. From tonic workouts, the 4 predictor variables explained insignificant amounts of post and delta BLa variance. Low tonic workout BLa ICC values may in part be responsible for the insignificant effect. However, with post-RE BLa as a criterion variable, phasic data showed a trend (p = 0.08) to explain the variance. Yet with delta BLa as our criterion, the 4 predictor variables collected from phasic workouts explained a significant (p < 0.05) degree of variance. Results yielded the following prediction equation: delta BLa = 1.40 + 1.116 (average acceleration set 1) - 0.011 (peak acceleration set 1) - 0.634 (average acceleration set 2) + 0.005 (peak acceleration set 2). The multiple R 2 value shows roughly 25% of the BLa variance was explained by this equation.

Table 4

Table 4

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Discussion

High-speed workouts like those done on the IET may induce more sport-specific adaptations in athletes than conditioning programs centered around standard RE equipment because of stark differences in movement velocities. For instance, whereas standard RE velocities for the squat average 2.0 rad · sec−1 (10), vertical jump countermovements typically attain knee angular velocities of 10.5 rad · sec−1 (29). Far greater knee angular velocities (20.7-39.4 rad · sec−1) occur from running and kicking motions by athletes (22,23,31). Although standard RE equipment workouts improve force output, without inclusion of a high-speed physical conditioning program, the athletes may inadvertently become slower, which undermines their performance in actual competition. Thus, because of sport-specific demands of modern-day competition, athletes may be better served by physical conditioning programs done at higher speeds, such as IET workouts, than those centered around standard RE equipment.

The current study examined acceleration as a predictor of BLa variance from IET workouts. Although acceleration-induced BLa increases have received little attention, the novelty of the IET design and operation has yielded surprising workout results. For instance, despite the light load imposed on users, 5 weeks of IET elbow flexor workouts caused significant concentric and eccentric peak torque gains (1). A comparison of phasic and tonic IET actions, which entailed kinematic and electromyographic (EMG) data collection, showed higher velocities, accelerations, antagonistic EMG activity, and smaller ranges of motion with phasic actions (30). Applied loads and EMG data were compared in 8 seated quadriceps RE done against 4 levels of resistance (21). Vastus medialis/lateralis EMG ratios from eccentric IET actions evoked higher values than the other RE, even those that imposed higher loads (21). Thus, with IET force and EMG data, it appears higher speeds and accelerations compensate for lighter loads (1,21,30). The IET is well suited for gains to high-speed sports-specific tasks like a baseball pitch, whereby a small mass is accelerated (25). Finally, a recent study compared RE workout variables from 2 inertia-based devices on their ability to predict BLa variance (5). Results showed IET variables were far more correlated to BLa variance than the other device examined (5). Continued inquiry into IET workouts is warranted.

Although prior studies have not specifically examined the impact of acceleration on BLa, its effect on performance was assessed in earlier work (4,13,17,20,29). Acceleration produced by impact exercise was revealed as a determinant of bone mineral density changes in premenopausal women (13). The effects of RE repetitions done at accelerated rates were compared to those done in a normal fashion on upper-body power changes to 2 groups of American college football players. Results revealed accelerated repetitions improved some upper-body power measures (17). Acceleration-accentuated conditioning programs also were examined for their effect on speed development (4,29). In addition to regular workouts, 8 weeks of additional resisted sprint training by rugby, soccer, and football players improved acceleration kinematics and gait (29), yet a similar group that also performed workouts without resisted sprints incurred comparable gains (29). Similar gains in acceleration occurred from elastic cord exercises geared toward faster sprint performance (4). A study that compared rotator cuff acceleration among 2 groups of athletes showed no significant differences existed among baseball players and controls (20). Thus, for greater acceleration in sport-specific skills, programs for athletes should emphasize bigger muscle groups normally recruited for gross motor tasks (4,20,29).

Studies done with standard RE equipment note factors such as the load imposed, work volume, and rest period duration affect BLa (2,7,32). Whereas repetition rates for standard equipment allow little acceleration, high-speed RE, albeit at constant angular velocities, was examined to note its affect on BLa (11,26). Experienced weight trainers subjected to 60-second bouts of knee extensor and flexor RE at 3 (0.52, 2.09, and 5.23 rad · sec−1) angular velocities showed BLa increased significantly at higher speeds (11). BLa increases corresponded to EMG changes incurred from RE (14). Other studies compared BLa changes from isokinetic RE done by strength and endurance athletes (24,26). Strength athletes consistently showed higher BLa post-RE vs. the endurance group (24,26). Reagan and Potteiger (26) showed higher post-RE BLa occurred at slower angular velocities, which is in disagreement with earlier work (11). Differences may result from the RE protocols used; Reagan and Potteiger workouts entailed 20 repetitions per velocity, whereas the Douris paradigm involved 60-second sets per velocity examined (11,26). Current results are most like those of Douris, perhaps as a result of similarities of the RE workout paradigms used (11).

In the current study, roughly 25% of the delta BLa variance from phasic workouts was accounted for by average and peak acceleration values and deserves further inquiry in future work. Acceleration may have led to greater reliance on anaerobic glycolysis that yielded higher BLa. Current results support our hypotheses whereby acceleration (a) described a significant degree of BLa variance and (b) phasic workouts evoked higher accelerations. Differences in the way phasic and tonic repetitions are performed likely accounts for higher phasic workout accelerations. Resistance is continually imposed over a full range of motion with tonic repetitions, whereas phasic workouts entailed oscillatory cord actions whereby the load was alternately imposed and removed over a given range of motion. IET weight sled mass is imposed on subjects by a nylon cord; when it is taut resistance is incurred, but as it becomes slack the load is removed. The portion of phasic repetitions that offer no weight sled resistance allows a large rate of movement increases and higher peak accelerations with the current phasic workouts.

With delta BLa as a criterion measure, phasic workout average acceleration values explained more variance than did peak acceleration. The strong delta BLa-average acceleration correlation from phasic workouts best represents the increase in the metabolite incurred from bouts of RE. Whereas peak accelerations represent the highest single value attained per 1-minute set, average accelerations are a more accurate indicator of the overall mean rate of movement increase, and the intensity of the RE effort, incurred from IET workouts. Thus, delta BLa and average acceleration values each provide a greater overall representation of changes incurred from phasic workouts, which likely explains why the 2 variables are highly correlated. Continued inquiry into the effects of acceleration and its impact on IET workouts is warranted.

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Practical Applications

The ability to accelerate, or increases in the rate of movement, is paramount for success in modern-day athletic competition. Rate of movement increases may cause greater reliance on anaerobic glycolysis that yield higher BLa and greater fatigue that subsequently impairs an athlete's ability to accelerate. This relationship is affirmed by current results, which show average acceleration values from 1-minute sets serve as a good predictor of delta BLa variance. For improved athletic performance, results suggest IET workouts as described herein may possibly improve an athlete's lactate threshold. Although such an adaptation could improve an athlete's ability to accelerate at higher BLa, it is important to note the current study did not measure lactate threshold. For those who rely on anaerobic glycolysis for adenosine triphosphate resynthesis, their coaches and trainers should tailor an athlete's workouts with respect to the muscles involved and the duration of exercise bouts for their chosen sport. When this occurs, workouts become more sport-specific to the athlete's needs and will lead to greater improvements.

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References

1. Albert, MS, Hillegass E, and Spiegel, P. Muscle torque changes caused by inertial exercise training. J Orthop Sports Phys Ther 20: 254-261, 1994.
2. Beneke, R, Hütler, M, Jung, M, and Leithaüser, R. Modeling the blood lactate kinetics at maximal short-term exercise conditions in children, adolescents, and adults. J Appl Physiol 99: 499-504, 1999.
3. Bishop, D. Evaluation of the Accusport lactate analyser. Int J Sports Med 22: 525-530, 2001.
4. Corn, RJ and Knudson, D. Effect of elastic-cord towing on the kinematics of the acceleration phase of sprinting. J Strength Cond Res 17: 72-75, 2003.
5. Caruso, JF, Coday, MA, Monda, JK, Roberts, KP, and Potter, WT. Body mass and exercise variable relationships to lactate derived from gravity-independent devices. Aviat Space Environ Med 78: 864-870, 2007.
6. Caruso, JF, Herron, JC, Capps, LB, Coday, MA, Ramsey, CA, and Drummond, JL. Blood lactate responses to leg presses performed against inertial resistance. Aviat Space Environ Med 77: 707-712, 2006.
7. Crewther, B, Cronin, J, and Keogh, J. Possible stimuli for strength and power adaptation. Sports Med 36: 65-78, 2006.
8. Davison, S. Inertial exercise clinical training instructional manual. Newman, GA: Engineering Marketing Association; 1997.
9. De Renne, C, Ho, K, and Murphy, J. Effects of general, special and specific resistance training on throwing velocity in baseball: a brief review. J Strength Cond Res 15: 148-156, 2001.
10. Donnelly, D, Berg, W, and Fiske, D. The effect of the direction of gaze on the kinematics of the squat exercise. J Strength Cond Res 20: 145-150, 2006.
11. Douris, PC. The effect of isokinetic exercise on the relationship between blood lactate and muscle fatigue. J Orthop Sports Phys Ther 17: 31-35, 1993.
12. Fichter, D. High speed eccentrics with inertial training. Available at: http://www.inno-sport.net/High%20Speed%20Eccentrics%20With%20Inertial%20Training.htm. 2007. Accessed July 24, 2009.
13. Heikkinen, R, Vihriala, E, Vainionpaa, A, Korpelainen, R, and Jamsa, T. Acceleration slope of exercise-induced impacts is a determinant of changes in bone density. J Biomech 40: 2967-2974, 2007.
14. Horita, T and Ishiko, T. Relationships between muscle lactate accumulation and surface EMG activities during isokinetic contractions in man. Eur J Appl Physiol Occup Physiol 56: 18-23, 1987.
15. http://impulsepower.com/testimonials.htm. Impulse Training Systems web site. Accessed July 20, 2009.
16. Jacobs, I, Tesch, P, Bar-Or, O, Karlsson, J, and Dotan, R. Lactate in human skeletal muscle after 10 and 30s of supramaximal exercise. J Appl Physiol 55: 365-367, 1983.
17. Jones, K, Hunter, G, Fleisig, G, Escamilla, R, and Lemak, L. The effects of compensatory acceleration on upper-body strength and power changes in collegiate football players. J Strength Cond Res 13: 99-105, 1999.
18. Kovaleski, JE, Heitman, RJ, Gurichek, LR, Erdmann, JW, and Trundle, TL. Reliability and effects of leg dominance on lower extremity isokinetic force and work using the closed chain rider system. J Sport Rehab 6: 319-326, 1997.
19. Kovaleski, JE, Ingersoll, CD, Knight, KL, and Mahar, CP. Reliability of the BTE Dynatrack isotonic dynamometer. Isok Exerc Sci 6: 41-43, 1996.
20. Manske, RC, Tajchman, CS, Stranghoner, TA, and Ellenbecker, TS. Difference in isokinetic torque acceleration energy of the rotator cuff: competitive male pitchers versus male nonathletes. J Strength Cond Res 18: 447-450, 2004.
21. Matheson, JW, Kernozek, TW, Denni, CW, and Davies, GJ. Electromyographic activity and applied load during seated quadriceps exercises. Med Sci Sports Exerc 33: 1713-1725, 2001.
22. Nunome, H, Asai, T, Ikegami, Y, and Sakurai, S. Three-dimensional kinetic analysis of side-foot and instep soccer kicks. Med Sci Sports Exerc 34: 2028-2036, 2002.
23. Nunome, H, Ikegami, Y, Kozakai, R, Apriantono, T, and Sano, S. Segmental dynamics of soccer instep kicking with the preferred and non-preferred leg. J Sport Sci Res 24: 529-541, 2006.
24. Paccotti, P, Minetto, M, Terzolo, M, Ventura, M, Ganzit, GP, Borrione, P, Termine, A, and Angeli, A. Effects of high-intensity isokinetic exercise on salivary cortisol in athletes with different training schedules: relationships to serum cortisol and lactate. Int J Sports Med 26: 747-755, 2005.
25. Pezzullo, D, Karas, S, and Irrgang, J. Functional plyometric exercises for the throwing athlete. J Ath Train 30: 22-26, 1995.
26. Regan, WF and Potteiger, JA. Isokinetic exercise velocities and blood lactate concentrations in strength/power and endurance athletes. J Strength Cond Res 13: 157-161, 1999.
27. Robergs, R, Ghiasvand, F, and Parker, D. Biochemistry of exercise-induced metabolic acidosis. Am J Physiol Reg Integ Comp Physiol 287: R502-R516, 2004.
    28. Rodacki, AL, Fowler, NE, and Bennet, SJ. Vertical jump coordination: fatigue effects. Med Sci Sports Exerc 34: 105-116, 2002.
    29. Spinks, CD, Murphy, AJ, Spinks, WL, and Lockie, RJ. The effects of resisted sprint training on acceleration performance and kinematics in soccer, rugby union, and Australian football players. J Strength Cond Res 21: 77-85, 2007.
    30. Tracy, J, Obuchi, S, and Johnson, B. Kinematics and electromyographic analysis of elbow flexion during inertial exercise. J Ath Train 30: 254-258, 1995.
    31. Vardaxis, V. The mechanical power analysis of the lower limb action during the recovery phase of the sprinting stride for advanced and intermediate sprinters master's thesis. Montreal, Canada: McGill University; 1988.
    32. Zaferidis, A, Smilos, I, Considine, R, and Tokmakidis, S. Serum leptin responses after acute resistance exercise protocols. J Appl Physiol 35: 591-597, 2002.
    Keywords:

    metabolism; inertia; velocity

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