MANIPULATION OF STEP HEIGHT AND ITS EFFECT LACTATE METABOLISM DURING A ONE-MINUTE ANAEROBIC STEP TEST BRIAN D. NGUYEN
AND
ON
TREVOR L. GILLUM
Department of Kinesiology, Exercise Physiology Laboratory, Exercise Science, California Baptist University, Riverside, California ABSTRACT
INTRODUCTION
Nguyen, BD and Gillum, TL. Manipulation of step height and its effect on lactate metabolism during a one-minute anaerobic step test. J Strength Cond Res 29(6): 1578–1583, 2015— The purpose of this study was to observe the effects of the 1-minute anaerobic step test on lactate production. In addition, a comparison of postexercise lactate levels between the traditional 40-cm step height and a modified 20-cm step height was tested along with multiple biomechanical components such as torque, knee angle, and power. A convenience sample of 9 healthy moderately trained individuals were recruited for this experiment. Each subject performed the 1-minute anaerobic step test in a counterbalanced, crossover, and repeated-measures design. They performed 2 trials, 1 with a 40-cm step height and another with a 20-cm step height. Results showed statistical significance in terms of the postexercise lactate concentration (40 cm: 8.04 6 2.13 mmol$L21; 20 cm: 6.18 6 2.62 mmol$L21) and lactate production (40 cm: 5.36 6 2.73 mmol$L21; 20 cm: 3.06 6 2.96 mmol$L21) between the 2 step heights (p # 0.05). With a lowered step height, the moment arm decreased significantly, which lowered the torque placed on the knee joint. Knee angle and power both decreased with a lowered step height of 20 cm. These results suggest that the 1-minute anaerobic step test is effective at eliciting lactate and can be used as an anaerobic exercise modality to train the anaerobic energy system. Furthermore, a step height of 40 cm seemed to be more effective at taxing the anaerobic energy system and eliciting lactate compared with a step height of 20 cm.
KEY WORDS moment arm, torque, knee angle, power, energy system
Address correspondence to Brian D. Nguyen, brianducbao.nguyen@ calbaptist.edu. 29(6)/1578–1583 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
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tepping exercises have been widely used to assess cardiovascular fitness, work, power, and heart rate responses. Tests such as the Harvard Step Test, Queen’s College Step test, and the 1-minute anaerobic step test have been proven effective at assessing these factors (15,16,25). These exercise protocols require concentric and eccentric contraction of the leg muscles, primarily the quadriceps. The Harvard Step test and Queen’s College Step Test have been proven effective at gauging aerobic fitness, whereas the 1-minute anaerobic step test is effective at assessing variables such as anaerobic power and work (16). However, there have been scarce amounts of research on the extent to which the 1-minute anaerobic step test taxes the anaerobic energy system. Default testing protocols for step exercises use a step that is approximately 40 cm high (5,16). This is the traditional height in both aerobic and anaerobic step exercises. One of the many disadvantages of using such an elevated step is the differing biomechanical components among individuals. Taller individuals would more likely have a less strenuous workout with this step height vs. shorter individuals due to the longer length of their limbs. Individuals with lower fitness levels would also have difficulty completing a step exercise with a step height of 40 cm due to the rapid onset of fatigue (3). With a higher step height, there is a higher potential risk of injury due to the constant ground reaction force being exerted on the leg (17). Therefore, by simply modifying the height of the step, the exercise can be tailored to individuals of varying heights and fitness levels as well as decrease the chance of sustaining injury. The primary objective for this study was to determine the efficacy by which the 1-minute anaerobic step test elicits a rise in lactate levels beyond the estimated threshold of 4 mmol$L21 in healthy moderately trained subjects. In so doing, the extent to which the step-test protocol stresses the anaerobic energy systems may be assessed (9,16). Furthermore, this test was used to compare lactate production with the use of a modified 20-cm step height vs. a traditional 40-cm step height. Blood lactate concentration is a primary determinant of exercise intensity and is greatly connected with high intermittent bursts of energy (4,8,11). The following hypotheses
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were tested: H1—both variations of the 1-minute anaerobic step test will be effective at eliciting a rise in blood lactate concentration above an estimated lactate threshold of 4 mmol$L21; H2—a lowered step height set to 20 cm will elicit a greater amount of lactate compared with the 40-cm step.
METHODS Experimental Approach to the Problem
Nine subjects underwent both the 40- and 20-cm step height intervention in a counterbalanced, crossover, and repeatedmeasures design to investigate the difference in lactate levels for both experimental trials. Before the experimental protocol, subjects were instructed on the proper stepping technique to minimize the risk of injury and to ensure the ability to produce maximal exertion. The 1-minute anaerobic step test was performed on a single leg. The subjects were allowed to choose which leg they preferred to use and the same leg was then used for both experimental trials. At least a week of recovery after the first trial was given to each subject before they began the second trial to ensure proper recovery of the fatigued leg muscles. The portable lactate plus meter (Nova Biomedical, Waltham, MA,) was used to measure pre- and post-exercise blood lactate levels. This device has been shown to be more favorable compared with other models and has been tested in both laboratory and field settings for its reliability and accuracy in measuring blood lactate concentration (12,24). Manipulation of the step height affected various biomechanical components of the exercise such as the knee angle, torque, and power. The components of torque consists of the moment arm, which is the perpendicular distance from the knee joint to the line of action of the force stemming from the center of mass (14,26). Power was calculated by taking the force of the subject in Newtons and multiplying that value by the distance traveled, which is the number of steps multiplied by the step height. This value was then divided by 60 seconds, which gave the power value in Newton meters per second (in Watts). Figure 1 illustrates the biomechanical components once the subject had assumed their position on the step. Subjects
Ages of all subjects ranged from 20 through 25 years of age. Age variable is shown on Table 1. IRB consents were signed and mentioned in highlighted text above. A convenience sample of 9 young, healthy, and moderately trained subjects, 5 men and 4 women, volunteered to participate in this study. Subjects who had sustained previous leg injuries, within the last 3 months before the experiment or had any inhibition to the range of motion of their leg were excluded from the study. Each subject had previous experience in performing moderate amounts of aerobic exercise per week. The frequency of exercise was approximately 3–4 days per week at moderate intensity. The mode of exercise was primarily aerobic and was performed for 30–60 minutes. In addition, subjects performed resistance training at low to moderate intensity approximately
Figure 1. Biomechanical components of stepping, including moment arm (MA), knee angle (KA), center of mass (COM), and force (N) during a default step height of 40 cm.
2 days per week. None of the appointed subjects were familiar at performing acute bouts of high-intensity exercise. This study was approved by the Office of Institutional Research, Planning, and Assessment. Subjects were then informed of the risks and procedures of the experiment through Institutional Review Board consent forms. Signatures from each subject were acquired before experimentation began. Before the experimental process, subject’s background information was recorded. Their average age, height, weight, and calculated body mass index are illustrated in Table 1. Procedures
One hour before entering the laboratory, subjects were instructed to abstain from ingesting any food and drink with the exception of water (10,18). Subjects’ daily and weekly diets were not monitored throughout the experiment. All 9 subjects underwent a standardized warm-up that was performed before the exercise test to lessen the risk of injury during the high-intensity bout of exercise. All subjects were
TABLE 1. Mean (6SD) of subject’s background information (n = 9). Variables
Measurements
Age (y) Height (cm) Weight (kg) Body mass index (kg$m22)
22.78 173.14 66.51 21.81
6 6 6 6
0.44 9.80 18.99 3.89
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Manipulation of Step Heights Effect on Lactate structed to assume their position on the step with their TABLE 2. Mean (6SD) and p values of various measured variables at each step chosen leg. The tibia was posiheight. tioned completely perpendicuStep height lar to the ground before the Variables (cm) Mean (6SD) p following measurements were taken: moment arm, step Resting lactate concentration 40 2.69 6 2.38 0.611 height, and knee angle. The (mmol$L21) 20 3.12 6 2.93 moment arm was measured Postexercise lactate concentration 40 8.04 6 2.13 0.019* (mmol$L21) 20 6.18 6 2.62 with a meter stick and was Lactate difference/production 40 5.36 6 2.73 0.001* the length from the axis of (post-minus rest) (mmol$L21) 20 3.06 6 2.96 rotation (knee joint) to the line Knee angle (degrees) 40 91.44 6 1.81 0.000* of action of the force, which 20 122.78 6 5.17 stems from the center of mass, Moment arm (cm) 40 38.44 6 2.31 0.000* 20 32.22 6 2.44 which was approximated to be Torque (N$m) 40 253.12 6 82.19 0.000* within the midabdominal 20 212.57 6 70.83 region (Figure 1). A goniomeNo. steps 40 55.67 6 12.33 0.001* ter was used to measure the 20 76.78 6 10.89 knee angle. Spotters were staPower (W) 40 243.61 6 94.49 0.001* 20 169.42 6 66.38 tioned behind each subject as a safety precaution in case of *Statistical significance between 40- and 20-cm step. falls and were instructed to count the number of steps that were performed. One step was counted whenever the subject reached 1808 knee extension and was elevated above the treated equally and were instructed to perform this warm-up step. Subjects then performed the exercise at maximal exerbefore performing the exercise on both the 40- and 20-cm tion and were instructed to perform as many steps as possistep height. The warm-up consisted of light stretching perble in 60 seconds. Once the 60 seconds had expired, they formed primarily with the quadriceps. Three repetitions of were carefully taken off the step and seated. An immediate static stretches were held for 30 seconds and performed on postexercise lactate reading was taken, and the number of each leg. The warm-up stretches were performed at very low steps was recorded. intensity so that there was no unnecessary muscle contraction that would cause a rise in lactate levels or a detriment to Statistical Analyses the subjects’ force or power production (13). Subjects were Before initiating this study, pilot data were collected (n = 3) then seated, and their ring fingers were pricked to obtain the using the identical set of procedures. The pilot data were resting blood lactate concentration. They were then inused to run a power analysis. The estimated sample size was 8 subjects, using an alpha level of 0.05 and a beta level of 0.80, to find differences between step heights. Statistical analysis was performed on each variable using Statistica (version 12; StatSoft, Inc., Tulsa, OK, USA). A dependent T-test was used to analyze the differences between the various variables for the 40- and 20-cm step heights, excluding force that remained constant throughout the experiment. A critical value Figure 2. Comparison of the biomechanical components of the 40- vs. 20-cm step height. Moment arm (MA), of 0.05 was established as staknee angle (KA), center of mass (COM), and force (N). tistically significant.
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Journal of Strength and Conditioning Research RESULTS Table 2 shows the various measured variables. The resting lactate concentration between the 40- and 20-cm steps showed no statistical significance (p . 0.05). However, there was a significantly greater postexercise lactate level during the 40-cm step height condition compared with the 20 cm. The difference in lactate production, from resting to postexercise, was greater for the 40-cm step height, with an average difference of approximately 2.3 mmol$L21 compared with the 20-cm step (p # 0.05). All subsequent variables yielded p values #0.05 (Table 2). A step height of 40 cm yielded an average knee angle of 91.448 compared with a 20-cm step height, which yielded an average knee angle of 122.788. Force was kept constant throughout the experiment and was simply the product of the subject’s weight and force of gravity (kg 3 9.81). The moment arm decreased approximately 6.22 cm as the step height was decreased from 40 to 20 cm. This then lowered the average torque. Subjects were able to perform, on average, approximately 21 less steps during the 40-cm step compared with the 20-cm step. Average absolute power increased during the 40-cm step vs. 20 by approximately 74.2 W.
DISCUSSION The results of this study suggests that a 1-minute anaerobic step test effectively raises blood lactate levels in moderately trained individuals regardless of a 20- or 40-cm step height. Both exercise interventions increased lactate concentrations well above the estimated lactate threshold of 4 mmol$L21 (9). These results were consistent with the first proposed hypothesis, which stated that the 1-minute anaerobic step test will elicit a rise in blood lactate concentration. However, statistical significance between the 2 step heights, regarding lactate production, suggests that the 40-cm step is greater in intensity and could be more effective at placing stress on the anaerobic energy system. Furthermore, the current findings demonstrating a significantly greater lactate response after the 40-cm step test compared with the 20-cm condition opposes our second hypothesis because a greater amount of lactate was produced during the 40-cm step despite the fact that fewer steps were performed by subjects on average. By manipulating the step height, the 2 components that changed significantly were the knee angle and torque. These 2 variables are the probable causes of the increase or decrease in exercise intensity, thereby affecting lactate metabolism. Studies have shown that changes in the range of motion and angle of contraction can either enhance or decrease the difficulty of an exercise, especially in power exercises such as the squat (22). In this study, statistical significance was observed between the knee angles of the 40- vs. 20-cm step. By setting the step height to 40 cm, the knee angle was reduced to an average of 918. This affected the quadriceps’ degree of contraction, causing subjects to contract their leg muscles an additional 898 to reach a full 1808 knee extension. This decreased knee
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angle made it more difficult for subjects to raise themselves above the step and complete 1 repetition. In contrast, the 20cm step yielded a knee angle of approximately 1238 on average. Therefore, to achieve 1808 knee extension, subjects would only have to contract their quadriceps an approximate 578, which made it easier to elevate themselves above the step and perform repetitions. Manipulation of torque can also influence the difficulty of an exercise. Studies have manipulated torque in exercises such as the push-up and isometric gripping to change their intensity and difficulty (19,23). Statistical difference was observed in this study between the torques of the 40- vs. 20-cm step. By lowering the step height, from 40 to 20 cm, the axis of rotation (knee joint) was brought approximately 6 cm closer to the line of action, which decreased the moment arm. Consequently, this decreased the torque and difficulty of the exercise. Figure 2 illustrates the change to the biomechanical components during both step heights. Lactate was the primary dependent variable that was measured in this study. It has been generally known that intermittent bouts of high-intensity exercises are able to cause lactate secretion from contracting muscle cells (1,4,21). This study showed that the use of the 1-minute anaerobic step test as an exercise modality, with a step height set at 40 cm, will produce higher amounts of blood lactate and is more difficult compared with the 20-cm step. Although subjects were able to perform 21 more steps on average with the 20-cm step, the lactate levels were lower compared with the 40-cm step. This suggests that the number of repetitions and the amount of muscle contraction are not the primary determinants of lactate production. Rather, it is the degree of contraction and torque on the knee joint that provides the intensity needed to elicit a rise in lactate. Power was also calculated in this experiment. Studies have documented the relationship between increasing lactate levels in high-power exercises such as judo kicks and power cleans (6,7). The components of power consisted of the height of the step, multiplied by with the force of the individual along with the number of steps that were performed. This product was then divided by 60 seconds, which was the allotted time given to perform the exercise. These data showed an increase in absolute power during the 40-cm step compared with the 20-cm step. This suggests that as power output increases, so too does lactate production, which is consistent with other studies. The limitations of this study included the small sample size and the population from which it was drawn. A recommendation for future studies is to test the effect of this exercise modality on elite level athletes and monitor their lactate response. To minimize the risk of further fatigue and injury, the step exercise was performed on only a single leg. This may have underestimated the lactate levels. Future studies should use both legs to observe the effects on lactate metabolism. Also, only 2 experimental trials were used for each subject and a single lactate VOLUME 29 | NUMBER 6 | JUNE 2015 |
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Manipulation of Step Heights Effect on Lactate reading was taken for pre- and post-exercise per trial. Future studies should use multiple experimental trials and acquire an average lactate value for pre- and post-exercise, which may provide more accurate results. Implementing more ways to measure exercise intensity such as heart rate monitors, Electrocardiogram, and Rate Perceived Exertion scales should also be done in future studies. In conclusion, the 1-minute anaerobic step test is effective at eliciting a rise in blood lactate concentration and pushing the anaerobic system well beyond the estimated lactate threshold of 4 mmol$L21. By simply lowering the height of the step, biomechanical factors such as torque and knee joint angle were significantly changed, which altered the intensity of the exercise, thereby resulting in changes to lactate production and repetitions performed. These data suggest that lactate production is more dependent on the degree of muscle contraction rather than the number of times the muscle contracts. This further suggests that the number of repetitions are secondary compared with intensity, workload, and power in terms of lactate production.
PRACTICAL APPLICATIONS Our findings demonstrate that the 1-minute anaerobic step test, performed with a step height set to 40 cm, is more intense and effective at eliciting a rise in blood lactate concentration, compared with a step height of 20 cm, due to the manipulation of the biomechanical components, such as torque and joint angle, thereby altering the economy of movement (20). Coaches and athletes who wish to enhance or measure anaerobic fitness and power production can use the test, set at the appropriate step height, to stress the anaerobic energy system. Additionally, this test could serve as an alternative to other high-intensity anaerobic exercises such as the Wingate Cycling Test because it uses a different mode of movement, stepping vs. cycling, and therefore can be used to train for sports that require a significant amount of anaerobic expenditure (basketball, volleyball, track and field, soccer, etc.). Furthermore, because the step test is an exercise that uses a single leg, it can be used as an exercise modality in clinical settings, specifically for patients who have experienced injuries on the opposite leg. The phenomenon is known as cross-education and refers to resistance training of a single limb, which consequently leads to strength increases of the untrained or injured limb on the contralateral side of the body (2,27). Results showed that lactate levels rose above the lactate threshold of 4 mmol$L21 for the 20-cm step, demonstrating that it was effective at stressing the anaerobic energy system. Therefore, by decreasing the step height and having patients perform the exercise on their uninjured leg, this could potentially result in a cross-education effect, which will allow patients to maintain strength while using a lowered step height to decrease the ground reaction force exerted on their injured limb.
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ACKNOWLEDGMENTS No funding was provided for this study. The author wishes to thank the 9 subjects who participated in this study for their utmost patience and co-operation. The authors specially thank the faculty advisor for promoting and supporting this research study. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
REFERENCES 1. Aedma, M, Timpmann, S, and Oopik, V. Effect of caffeine on upper body anaerobic performance in wrestlers in simulated competitionday conditions. Int J Sport Nutr Exerc Metab 23: 601–609, 2013. 2. Baker, D. Non-running, high-intensity energy- system conditioning cross-training workouts for injured athletes. J Aust Strength Cond 22: 39–44, 2014. 3. Bandyopadhyay, A. Queen’s college step test- an alternative of harvard step test in young Indian men. Int J Appl Sports Sci 19: 1–6, 2007. 4. Bangsbo, J, Madsen, K, Kien, B, and Ritcher, EA. Effect of muscle acidity on muscle metabolism and fatigue during intense exercise in man. J Physiol 495: 587–596, 1996. 5. Chen, S, Wang, J, Lee, W, Hou, C, Chen, C, Laio, Y, Lin, C, and Kuo, C. Validitiy of the 3 min step test in moderate altitude: Environment temperature as a confounder. Appl Physiol Nutr Metab 31: 726–730, 2006. 6. Date, AS, Simonson, SR, Ransdell, LB, and Gao, Y. Lactate response to different volume patterns of power clean. J Strength Cond Res 27: 604–610, 2013. 7. Dominguez, JB, Bonitch-Gongora, J, Padial, P, and Feriche, B. Changes in peak leg power induced by successive judo bouts and their relationship to lactate production. J Sports Sci 28: 1527–1534, 2010. 8. Fabre, N, Mourot, L, Zerbini, L, Pellegrini, B, Bortolan, L, and Schena, F. A novel approach for lactate threshold assessment based of rate of perceived exertion. Int J Sports Physiol Perform 8: 263–270, 2013. 9. Fernandes, RJ, Sousa, M, Pinheiro, A, Vilar, S, Colaco, P, and VilasBoas, P. Assessment of individual anaerobic threshold and stroking parameters in swimmers aged 10-11 years. Eur J Sport Sci 10: 311– 317, 2010. 10. Fry, AC, Bloomer, RJ, Falvo, MJ, Moore, CA, Schilling, BK, and Weiss, LW. Effect of a liquid multivitamin/mineral supplement on anaerobic exercise performance. Res Sports Med 14: 53–64, 2006. 11. Guru, K, Gourang, SA, and Singh, SJ. Effect of active arm exercise and passive rest in physiological recovery after high intensity exercise. Biol Exerc 9: 10–22, 2013. 12. Hart, S, Drevets, K, Alford, M, Salacinski, A, and Hunt, BE. A method-comparison study regarding the validity and reliability of the lactate plus analyzer. BMJ Open 3: 1–7, 2013. 13. Kay, AD and Blazevich, AJ. Effect of acute static stretch on maximal muscle performance: A systematic review. Med Sci Sports Exerc 44: 154–156, 2012. 14. Lategan, L. Differences in knee flexion and extension angles of peak torque between men and women. Isokinet Exerc Sci 20: 71–76, 2012. 15. Lubans, DR, Morgan, PJ, Callister, R, and Collins, CE. The relationship between pedometer step counts and estimated VO2 Max as determined by submaximal fitness test in adolescents. Pediatr Exerc Sci 20: 273–284, 2008. 16. Manahan, JE and Shultz, BB. The one-minute step test as a measure of 600-yard run performance. Res Q 42: 173–177, 1989. 17. McEldowney, KM, Hopper, LS, Etlin-Stein, H, and Redding, E. Fatigue effects on quadriceps and hamstrings activation in dancers performing drop landings. J Dance Med Sci 17: 109–114, 2013.
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Journal of Strength and Conditioning Research 18. Millard-Stafford, ML, Brown, MB, and Snow, TK. Acute carbohydrate ingestion affects lactate response in highly trained swimmers. Int J Sports Physiol Perform 5: 42–54, 2010. 19. Negrete, RJ, Hanney, WJ, Pabian, P, and Kolber, MJ. Upper body push and pull strength ratio in recreationally active adults. Int J Sports Phys Ther 8: 138–144, 2013. 20. Nelson, WL. Physical principles of economies of skilled movements. Biol Cybern 46: 135–147, 1983. 21. Poole, DC and Gaesser, GA. Response of ventilatory and lactate thresholds to continuous and interval training. J Appl Physiol (1985) 58: 1115–1121, 1985. 22. Sato, K, Fortenbaugh, D, Hydock, DS, and Helse, GD. Comparison of back squat kinematics between barefoot and shoe conditions. Int J Sports Sci Coach 8: 571–578, 2013. 23. Slota, GP, Suh, MS, Latash, ML, and Zatsiorsky, VM. Stability control of grasping objects with different locations
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of center of mass and rotational inertia. J Mot Behav 44: 169–178, 2012. 24. Tanner, RK, Full, KL, and Ross, ML. Evaluation of three portable blood lactate analysers: Lacate Pro, Lactate Scout and Lactate Plus. Eur J Appl Physiol 109: 551–559, 2010. 25. Toriola, AL and Mathur, DN. Relationship between harvard step test and cooper’s twelve-minute run/walk test in determining cardiorespiratory endurance in nonathletic females. SNIPES J 9: 54–57, 1986. 26. Wurdeman, SR, Huisinga, JM, Filipi, M, and Stergiou, N. Multiple sclerosis alters the mechanical work performed on the body’s center of mass during gait. J Appl Biomech 29: 435–442, 2013. 27. Zult, T, Howatson, G, Kadar, EE, Farthing, JP, and Hortobagyi, T. Role of mirror-neuron system in cross education. Sports Med 44: 159–178, 2014.
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AND
ON
TREVOR L. GILLUM
Department of Kinesiology, Exercise Physiology Laboratory, Exercise Science, California Baptist University, Riverside, California ABSTRACT
INTRODUCTION
Nguyen, BD and Gillum, TL. Manipulation of step height and its effect on lactate metabolism during a one-minute anaerobic step test. J Strength Cond Res 29(6): 1578–1583, 2015— The purpose of this study was to observe the effects of the 1-minute anaerobic step test on lactate production. In addition, a comparison of postexercise lactate levels between the traditional 40-cm step height and a modified 20-cm step height was tested along with multiple biomechanical components such as torque, knee angle, and power. A convenience sample of 9 healthy moderately trained individuals were recruited for this experiment. Each subject performed the 1-minute anaerobic step test in a counterbalanced, crossover, and repeated-measures design. They performed 2 trials, 1 with a 40-cm step height and another with a 20-cm step height. Results showed statistical significance in terms of the postexercise lactate concentration (40 cm: 8.04 6 2.13 mmol$L21; 20 cm: 6.18 6 2.62 mmol$L21) and lactate production (40 cm: 5.36 6 2.73 mmol$L21; 20 cm: 3.06 6 2.96 mmol$L21) between the 2 step heights (p # 0.05). With a lowered step height, the moment arm decreased significantly, which lowered the torque placed on the knee joint. Knee angle and power both decreased with a lowered step height of 20 cm. These results suggest that the 1-minute anaerobic step test is effective at eliciting lactate and can be used as an anaerobic exercise modality to train the anaerobic energy system. Furthermore, a step height of 40 cm seemed to be more effective at taxing the anaerobic energy system and eliciting lactate compared with a step height of 20 cm.
KEY WORDS moment arm, torque, knee angle, power, energy system
Address correspondence to Brian D. Nguyen, brianducbao.nguyen@ calbaptist.edu. 29(6)/1578–1583 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
1578
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S
tepping exercises have been widely used to assess cardiovascular fitness, work, power, and heart rate responses. Tests such as the Harvard Step Test, Queen’s College Step test, and the 1-minute anaerobic step test have been proven effective at assessing these factors (15,16,25). These exercise protocols require concentric and eccentric contraction of the leg muscles, primarily the quadriceps. The Harvard Step test and Queen’s College Step Test have been proven effective at gauging aerobic fitness, whereas the 1-minute anaerobic step test is effective at assessing variables such as anaerobic power and work (16). However, there have been scarce amounts of research on the extent to which the 1-minute anaerobic step test taxes the anaerobic energy system. Default testing protocols for step exercises use a step that is approximately 40 cm high (5,16). This is the traditional height in both aerobic and anaerobic step exercises. One of the many disadvantages of using such an elevated step is the differing biomechanical components among individuals. Taller individuals would more likely have a less strenuous workout with this step height vs. shorter individuals due to the longer length of their limbs. Individuals with lower fitness levels would also have difficulty completing a step exercise with a step height of 40 cm due to the rapid onset of fatigue (3). With a higher step height, there is a higher potential risk of injury due to the constant ground reaction force being exerted on the leg (17). Therefore, by simply modifying the height of the step, the exercise can be tailored to individuals of varying heights and fitness levels as well as decrease the chance of sustaining injury. The primary objective for this study was to determine the efficacy by which the 1-minute anaerobic step test elicits a rise in lactate levels beyond the estimated threshold of 4 mmol$L21 in healthy moderately trained subjects. In so doing, the extent to which the step-test protocol stresses the anaerobic energy systems may be assessed (9,16). Furthermore, this test was used to compare lactate production with the use of a modified 20-cm step height vs. a traditional 40-cm step height. Blood lactate concentration is a primary determinant of exercise intensity and is greatly connected with high intermittent bursts of energy (4,8,11). The following hypotheses
TM
Journal of Strength and Conditioning Research
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
the
TM
Journal of Strength and Conditioning Research
| www.nsca.com
were tested: H1—both variations of the 1-minute anaerobic step test will be effective at eliciting a rise in blood lactate concentration above an estimated lactate threshold of 4 mmol$L21; H2—a lowered step height set to 20 cm will elicit a greater amount of lactate compared with the 40-cm step.
METHODS Experimental Approach to the Problem
Nine subjects underwent both the 40- and 20-cm step height intervention in a counterbalanced, crossover, and repeatedmeasures design to investigate the difference in lactate levels for both experimental trials. Before the experimental protocol, subjects were instructed on the proper stepping technique to minimize the risk of injury and to ensure the ability to produce maximal exertion. The 1-minute anaerobic step test was performed on a single leg. The subjects were allowed to choose which leg they preferred to use and the same leg was then used for both experimental trials. At least a week of recovery after the first trial was given to each subject before they began the second trial to ensure proper recovery of the fatigued leg muscles. The portable lactate plus meter (Nova Biomedical, Waltham, MA,) was used to measure pre- and post-exercise blood lactate levels. This device has been shown to be more favorable compared with other models and has been tested in both laboratory and field settings for its reliability and accuracy in measuring blood lactate concentration (12,24). Manipulation of the step height affected various biomechanical components of the exercise such as the knee angle, torque, and power. The components of torque consists of the moment arm, which is the perpendicular distance from the knee joint to the line of action of the force stemming from the center of mass (14,26). Power was calculated by taking the force of the subject in Newtons and multiplying that value by the distance traveled, which is the number of steps multiplied by the step height. This value was then divided by 60 seconds, which gave the power value in Newton meters per second (in Watts). Figure 1 illustrates the biomechanical components once the subject had assumed their position on the step. Subjects
Ages of all subjects ranged from 20 through 25 years of age. Age variable is shown on Table 1. IRB consents were signed and mentioned in highlighted text above. A convenience sample of 9 young, healthy, and moderately trained subjects, 5 men and 4 women, volunteered to participate in this study. Subjects who had sustained previous leg injuries, within the last 3 months before the experiment or had any inhibition to the range of motion of their leg were excluded from the study. Each subject had previous experience in performing moderate amounts of aerobic exercise per week. The frequency of exercise was approximately 3–4 days per week at moderate intensity. The mode of exercise was primarily aerobic and was performed for 30–60 minutes. In addition, subjects performed resistance training at low to moderate intensity approximately
Figure 1. Biomechanical components of stepping, including moment arm (MA), knee angle (KA), center of mass (COM), and force (N) during a default step height of 40 cm.
2 days per week. None of the appointed subjects were familiar at performing acute bouts of high-intensity exercise. This study was approved by the Office of Institutional Research, Planning, and Assessment. Subjects were then informed of the risks and procedures of the experiment through Institutional Review Board consent forms. Signatures from each subject were acquired before experimentation began. Before the experimental process, subject’s background information was recorded. Their average age, height, weight, and calculated body mass index are illustrated in Table 1. Procedures
One hour before entering the laboratory, subjects were instructed to abstain from ingesting any food and drink with the exception of water (10,18). Subjects’ daily and weekly diets were not monitored throughout the experiment. All 9 subjects underwent a standardized warm-up that was performed before the exercise test to lessen the risk of injury during the high-intensity bout of exercise. All subjects were
TABLE 1. Mean (6SD) of subject’s background information (n = 9). Variables
Measurements
Age (y) Height (cm) Weight (kg) Body mass index (kg$m22)
22.78 173.14 66.51 21.81
6 6 6 6
0.44 9.80 18.99 3.89
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Manipulation of Step Heights Effect on Lactate structed to assume their position on the step with their TABLE 2. Mean (6SD) and p values of various measured variables at each step chosen leg. The tibia was posiheight. tioned completely perpendicuStep height lar to the ground before the Variables (cm) Mean (6SD) p following measurements were taken: moment arm, step Resting lactate concentration 40 2.69 6 2.38 0.611 height, and knee angle. The (mmol$L21) 20 3.12 6 2.93 moment arm was measured Postexercise lactate concentration 40 8.04 6 2.13 0.019* (mmol$L21) 20 6.18 6 2.62 with a meter stick and was Lactate difference/production 40 5.36 6 2.73 0.001* the length from the axis of (post-minus rest) (mmol$L21) 20 3.06 6 2.96 rotation (knee joint) to the line Knee angle (degrees) 40 91.44 6 1.81 0.000* of action of the force, which 20 122.78 6 5.17 stems from the center of mass, Moment arm (cm) 40 38.44 6 2.31 0.000* 20 32.22 6 2.44 which was approximated to be Torque (N$m) 40 253.12 6 82.19 0.000* within the midabdominal 20 212.57 6 70.83 region (Figure 1). A goniomeNo. steps 40 55.67 6 12.33 0.001* ter was used to measure the 20 76.78 6 10.89 knee angle. Spotters were staPower (W) 40 243.61 6 94.49 0.001* 20 169.42 6 66.38 tioned behind each subject as a safety precaution in case of *Statistical significance between 40- and 20-cm step. falls and were instructed to count the number of steps that were performed. One step was counted whenever the subject reached 1808 knee extension and was elevated above the treated equally and were instructed to perform this warm-up step. Subjects then performed the exercise at maximal exerbefore performing the exercise on both the 40- and 20-cm tion and were instructed to perform as many steps as possistep height. The warm-up consisted of light stretching perble in 60 seconds. Once the 60 seconds had expired, they formed primarily with the quadriceps. Three repetitions of were carefully taken off the step and seated. An immediate static stretches were held for 30 seconds and performed on postexercise lactate reading was taken, and the number of each leg. The warm-up stretches were performed at very low steps was recorded. intensity so that there was no unnecessary muscle contraction that would cause a rise in lactate levels or a detriment to Statistical Analyses the subjects’ force or power production (13). Subjects were Before initiating this study, pilot data were collected (n = 3) then seated, and their ring fingers were pricked to obtain the using the identical set of procedures. The pilot data were resting blood lactate concentration. They were then inused to run a power analysis. The estimated sample size was 8 subjects, using an alpha level of 0.05 and a beta level of 0.80, to find differences between step heights. Statistical analysis was performed on each variable using Statistica (version 12; StatSoft, Inc., Tulsa, OK, USA). A dependent T-test was used to analyze the differences between the various variables for the 40- and 20-cm step heights, excluding force that remained constant throughout the experiment. A critical value Figure 2. Comparison of the biomechanical components of the 40- vs. 20-cm step height. Moment arm (MA), of 0.05 was established as staknee angle (KA), center of mass (COM), and force (N). tistically significant.
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Journal of Strength and Conditioning Research RESULTS Table 2 shows the various measured variables. The resting lactate concentration between the 40- and 20-cm steps showed no statistical significance (p . 0.05). However, there was a significantly greater postexercise lactate level during the 40-cm step height condition compared with the 20 cm. The difference in lactate production, from resting to postexercise, was greater for the 40-cm step height, with an average difference of approximately 2.3 mmol$L21 compared with the 20-cm step (p # 0.05). All subsequent variables yielded p values #0.05 (Table 2). A step height of 40 cm yielded an average knee angle of 91.448 compared with a 20-cm step height, which yielded an average knee angle of 122.788. Force was kept constant throughout the experiment and was simply the product of the subject’s weight and force of gravity (kg 3 9.81). The moment arm decreased approximately 6.22 cm as the step height was decreased from 40 to 20 cm. This then lowered the average torque. Subjects were able to perform, on average, approximately 21 less steps during the 40-cm step compared with the 20-cm step. Average absolute power increased during the 40-cm step vs. 20 by approximately 74.2 W.
DISCUSSION The results of this study suggests that a 1-minute anaerobic step test effectively raises blood lactate levels in moderately trained individuals regardless of a 20- or 40-cm step height. Both exercise interventions increased lactate concentrations well above the estimated lactate threshold of 4 mmol$L21 (9). These results were consistent with the first proposed hypothesis, which stated that the 1-minute anaerobic step test will elicit a rise in blood lactate concentration. However, statistical significance between the 2 step heights, regarding lactate production, suggests that the 40-cm step is greater in intensity and could be more effective at placing stress on the anaerobic energy system. Furthermore, the current findings demonstrating a significantly greater lactate response after the 40-cm step test compared with the 20-cm condition opposes our second hypothesis because a greater amount of lactate was produced during the 40-cm step despite the fact that fewer steps were performed by subjects on average. By manipulating the step height, the 2 components that changed significantly were the knee angle and torque. These 2 variables are the probable causes of the increase or decrease in exercise intensity, thereby affecting lactate metabolism. Studies have shown that changes in the range of motion and angle of contraction can either enhance or decrease the difficulty of an exercise, especially in power exercises such as the squat (22). In this study, statistical significance was observed between the knee angles of the 40- vs. 20-cm step. By setting the step height to 40 cm, the knee angle was reduced to an average of 918. This affected the quadriceps’ degree of contraction, causing subjects to contract their leg muscles an additional 898 to reach a full 1808 knee extension. This decreased knee
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angle made it more difficult for subjects to raise themselves above the step and complete 1 repetition. In contrast, the 20cm step yielded a knee angle of approximately 1238 on average. Therefore, to achieve 1808 knee extension, subjects would only have to contract their quadriceps an approximate 578, which made it easier to elevate themselves above the step and perform repetitions. Manipulation of torque can also influence the difficulty of an exercise. Studies have manipulated torque in exercises such as the push-up and isometric gripping to change their intensity and difficulty (19,23). Statistical difference was observed in this study between the torques of the 40- vs. 20-cm step. By lowering the step height, from 40 to 20 cm, the axis of rotation (knee joint) was brought approximately 6 cm closer to the line of action, which decreased the moment arm. Consequently, this decreased the torque and difficulty of the exercise. Figure 2 illustrates the change to the biomechanical components during both step heights. Lactate was the primary dependent variable that was measured in this study. It has been generally known that intermittent bouts of high-intensity exercises are able to cause lactate secretion from contracting muscle cells (1,4,21). This study showed that the use of the 1-minute anaerobic step test as an exercise modality, with a step height set at 40 cm, will produce higher amounts of blood lactate and is more difficult compared with the 20-cm step. Although subjects were able to perform 21 more steps on average with the 20-cm step, the lactate levels were lower compared with the 40-cm step. This suggests that the number of repetitions and the amount of muscle contraction are not the primary determinants of lactate production. Rather, it is the degree of contraction and torque on the knee joint that provides the intensity needed to elicit a rise in lactate. Power was also calculated in this experiment. Studies have documented the relationship between increasing lactate levels in high-power exercises such as judo kicks and power cleans (6,7). The components of power consisted of the height of the step, multiplied by with the force of the individual along with the number of steps that were performed. This product was then divided by 60 seconds, which was the allotted time given to perform the exercise. These data showed an increase in absolute power during the 40-cm step compared with the 20-cm step. This suggests that as power output increases, so too does lactate production, which is consistent with other studies. The limitations of this study included the small sample size and the population from which it was drawn. A recommendation for future studies is to test the effect of this exercise modality on elite level athletes and monitor their lactate response. To minimize the risk of further fatigue and injury, the step exercise was performed on only a single leg. This may have underestimated the lactate levels. Future studies should use both legs to observe the effects on lactate metabolism. Also, only 2 experimental trials were used for each subject and a single lactate VOLUME 29 | NUMBER 6 | JUNE 2015 |
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Manipulation of Step Heights Effect on Lactate reading was taken for pre- and post-exercise per trial. Future studies should use multiple experimental trials and acquire an average lactate value for pre- and post-exercise, which may provide more accurate results. Implementing more ways to measure exercise intensity such as heart rate monitors, Electrocardiogram, and Rate Perceived Exertion scales should also be done in future studies. In conclusion, the 1-minute anaerobic step test is effective at eliciting a rise in blood lactate concentration and pushing the anaerobic system well beyond the estimated lactate threshold of 4 mmol$L21. By simply lowering the height of the step, biomechanical factors such as torque and knee joint angle were significantly changed, which altered the intensity of the exercise, thereby resulting in changes to lactate production and repetitions performed. These data suggest that lactate production is more dependent on the degree of muscle contraction rather than the number of times the muscle contracts. This further suggests that the number of repetitions are secondary compared with intensity, workload, and power in terms of lactate production.
PRACTICAL APPLICATIONS Our findings demonstrate that the 1-minute anaerobic step test, performed with a step height set to 40 cm, is more intense and effective at eliciting a rise in blood lactate concentration, compared with a step height of 20 cm, due to the manipulation of the biomechanical components, such as torque and joint angle, thereby altering the economy of movement (20). Coaches and athletes who wish to enhance or measure anaerobic fitness and power production can use the test, set at the appropriate step height, to stress the anaerobic energy system. Additionally, this test could serve as an alternative to other high-intensity anaerobic exercises such as the Wingate Cycling Test because it uses a different mode of movement, stepping vs. cycling, and therefore can be used to train for sports that require a significant amount of anaerobic expenditure (basketball, volleyball, track and field, soccer, etc.). Furthermore, because the step test is an exercise that uses a single leg, it can be used as an exercise modality in clinical settings, specifically for patients who have experienced injuries on the opposite leg. The phenomenon is known as cross-education and refers to resistance training of a single limb, which consequently leads to strength increases of the untrained or injured limb on the contralateral side of the body (2,27). Results showed that lactate levels rose above the lactate threshold of 4 mmol$L21 for the 20-cm step, demonstrating that it was effective at stressing the anaerobic energy system. Therefore, by decreasing the step height and having patients perform the exercise on their uninjured leg, this could potentially result in a cross-education effect, which will allow patients to maintain strength while using a lowered step height to decrease the ground reaction force exerted on their injured limb.
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ACKNOWLEDGMENTS No funding was provided for this study. The author wishes to thank the 9 subjects who participated in this study for their utmost patience and co-operation. The authors specially thank the faculty advisor for promoting and supporting this research study. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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