JOURNAL OF SPORTS SCIENCE & MEDICINE |
Research article |
VALIDITY OF A COMMERCIAL LINEAR ENCODER TO ESTIMATE BENCH PRESS 1 RM FROM THE FORCE-VELOCITY RELATIONSHIP | |||||||||
Laurent Bosquet1,2,3, Jeremy Porta-Benache1 and Jérôme Blais2 | |||||||||
1Faculty of Sport Sciences, University of Poitiers, Poitiers, France, 2Department of Kinesiology, University of Montreal, Montreal, Canada, 3Sport Experts association, Poitiers, France. | |||||||||
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© Journal of Sports Science and Medicine (2010) 9, 459 - 463 | |||||||||
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ABSTRACT | |||||||||||||
The aim of this study was to assess the validity and accuracy of a commercial linear encoder (Musclelab, Ergotest, Norway) to estimate Bench press 1 repetition maximum (1RM) from the force - velocity relationship. Twenty seven physical education students and teachers (5 women and 22 men) with a heterogeneous history of strength training participated in this study. They performed a 1 RM test and a force - velocity test using a Bench press lifting task in a random order. Mean 1 RM was 61.8 ± 15.3 kg (range: 34 to 100 kg), while 1 RM estimated by the Musclelab's software from the force-velocity relationship was 56.4 ± 14.0 kg (range: 33 to 91 kg). Actual and estimated 1 RM were very highly correlated (r = 0.93, p<0.001) but largely different (Bias: 5.4 ± 5.7 kg, p < 0.001, ES = 1.37). The 95% limits of agreement were ±11.2 kg, which represented ±18% of actual 1 RM. It was concluded that 1 RM estimated from the force-velocity relationship was a good measure for monitoring training induced adaptations, but also that it was not accurate enough to prescribe training intensities. Additional studies are required to determine whether accuracy is affected by age, sex or initial level. Key words: Muscle strength diagnosis, performance prediction, innovative technology. |
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INTRODUCTION | |||||||||||||
The ability to develop high levels of force to accelerate or decelerate a limb or an external load of constant mass, usually defined as isoinertial strength (Abernethy and Jürimäe, 1996), is a major determinant of performance in many sports. It is therefore not surprising to observe that the development of maximal isoinertial strength is given a high priority in conditioning programs (Baechle and Earle, 2008). Optimal strength development requires not only a sound understanding of the mechanisms underlying maximal isoinertial strength and a repertoire of strategies to enhance these underlying factors, but also valid and reliable tests and measures to assess this specific component of physical fitness. |
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METHODS | |||||||||||||
Following a thorough briefing all participants signed a written statement of informed consent. They completed a Bench press 1 RM test and a Bench press force - velocity test in a random order. Both tests were separated by at least 48 hours and were performed in a 10 - day period. To avoid any residual fatigue induced by recent training, participants were asked to refrain from strenuous exercise the day before the tests. They were also asked to arrive fully hydrated to the laboratory, at least three hours after their last meal. No attempt was made to control the content of this meal. Bench press force-velocity test Statistical analysis where ES is the effect size, M1 and M2 are the mean of actual and estimated 1RM, r is the product moment correlation of the two sets of data, and SDpooled is the pooled standard deviation, calculated as follows: where S12 and S22 are the variance of actual and estimated 1 RM, and n is the number of participants. The magnitude of the difference was considered either small (0.2 < ES < 0.5), moderate (0.5 < ES < 0.8), or large (ES > 0.8) (Cohen, 1988). A posteriori power analysis indicated that 27 participants per group would result in a 99% chance of obtaining statistical significance at the 0.05 level for the 1.37 effect size observed in this study. Pearson product moment correlation was used to evaluate the association between the two measures of 1 RM. We considered a correlation over 0.90 as very high, between 0.70 and 0.89 as high and between 0.50 and 0.69 as moderate (Munro, 1997). The 95% limits of agreement were calculated according the method of Bland and Altman (Bland and Altman, 1986). Statistical significance level was set at p < 0.05. All calculations were made with Statistica 6.0 (Statsoft, Tulsa, USA). |
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RESULTS | |||||||||||||
The number of trials required to detect 1 RM was 4 ± 1 (range: 3 to 6). Mean 1 RM was 61.8 ± 15.3 kg (range: 34 to 100 kg). The number of trials required to obtain the force - velocity relationship was 10 ± 2 (range: 5 to 14). The average curve of participants who were able to perform at least 10 trials (n =19) is presented in Figure 1. Mean Ppeak of the overall sample was 265 ± 59 W (range: 86 to 407 W) and was reached at 48 ± 9% of actual 1 RM (range: 35 to 65%). Mean 1 RM estimated from the force velocity relationship by the Musclelab's software was 56.4 ± 14.0 kg (range: 33 to 91 kg). Actual and estimated 1 RM were very highly correlated (Figure 2; r = 0.93, p < 0.001) but largely different (Bias: 5.4 ± 5.7 kg, p < 0.001, ES = 1.37). The 95% limits of agreement were ±11.2 kg (i. e. ± 18% of actual 1 RM), thus suggesting that the difference between actual and estimated 1 RM will lie between these limits in 95 of 100 new individuals performing these tests. The linear regression equation of the relationship between actual and estimated 1 RM (Figure 2) was: y = 1.02x + 4.25 where x and y represent estimated and actual 1 RM (kg), respectively. Adjusted coefficient of determination was 0.98 and the standard error of estimate (SEE) was 5.83 kg. |
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DISCUSSION | |||||||||||||
The aim of this study was to assess the validity and accuracy of a commercial linear encoder (Musclelab, Ergotest, Norway) to estimate Bench press 1 RM from the force - velocity relationship. Our main finding was the high validity of this estimation, together with a questionable accuracy. Interestingly, the correlation and 95% limits of agreement computed in our study compare very well with data published in two recent reports. |
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ACKNOWLEDGEMENTS | |
No funds were received for this work from any organizations and the authors have no conflicts of interest directly relevant to the content of this paper. |
AUTHORS BIOGRAPHY | |
Laurent BOSQUET Employment: Professor, Faculty of sport sciences, University of Poitiers (France), Associate professor, Department of kinesiology, University of Montreal (Canada) Degree: PhD Research interests: Exercise physiology, aerobic and anaerobic capacity, autonomic control of heart rate, overreaching. E-mail: laurent.bosquet@univ-poitiers.fr | |
Jeremy PORTA-BENACHE Employment: Student (Master degree), Faculty of sport sciences, University of Poitiers (France) Degree: BSc Research interests: Strength, power, repeated sprint ability. E-mail: jeremy.porta-benache@etu.univ-poitiers.fr | |
Jerome BLAIS Employment: Student (Master degree), Department of education sciences, University of Montreal (Canada) Degree: BSc Research interests: Strength, power. E-mail: Jerome.blais@umontreal.ca |