Within-subject consistency of unimodal and bimodal force application during the countermovement jump

Countermovement jump (CMJ) force data are often time-normalized so researchers and practitioners can study the effect that sex, training status, and training intervention have on CMJ strategy, the so-called force-time curve shape. Data are often collected on an individual basis and then averaged across groups of interest. However, little is known about the within-subject agreement of the CMJ force-time curve shape, and this formed the aim of this study. Fifteen men performed 10 CMJs on in-ground force plates, force-time curves were plotted, and their shape categorized as exhibiting either a single peak (unimodal) or a double peak (bimodal). Percentage agreement and the kappa coefficient were used to assess within-subject agreement. Over two and three trials 13% demonstrated a unimodal shape, 67% exhibited a bimodal shape, and 20% were inconsistent. When five trials were considered the unimodal shape was not demonstrated consistently, 67% demonstrated a bimodal shape, and 33% were inconsistent. Over 10 trials none demonstrated the unimodal shape, 60% demonstrated the bimodal shape, and 40% were inconsistent. The results of this study suggest that researchers and practitioners should ensure within-subject consistency before group averaging CMJ force-time data to help avoid errors that not doing so may cause

KINETIC ANALYSIS OF A UNILATERAL SNATCH MOVEMENT

The vertical ground reaction force (VGRF) of 7 weightlifters performing one-handed dumbbell power snatches with loads of 80%, 90% and 100% of 1RM were recorded at 500 Hz from 2 Kistler force platforms. There were no significant load or side effects for the pull phase peak VGRF or catch loading rates (P>0.05), although with the exception of the catch loading rate for the heaviest loads, non-lifting side values tended to be larger than those of the lifting side. In addition to this, lifting side pull phase duration was significantly longer than the non-lifting side (

EXPLORING THE BIOMECHANICAL CHARACTERISTICS OF THE WEIGHTLIFTING JERK

The vertical ground reaction force (VGRF) and front foot sagittal plane movement of the weightlifting jerk were recorded from seven weightlifters. Average knee flexion during the dip phase was 58 ± 9 degrees (mean ± SD) at an average angular velocity of 125 ± 16 degrees.s-1 exerting a vertical impulse of 138 ± 17.3 Ns. The peak rate of force development was 17.2 ± 4.86 BW.s-1, the VGRF continuing to increase from a propulsion impulse of 113.7 ± 31.2 Ns to a peak drive phase value of 3.5 ± 1.2 BW, extending the knees by 54 ± 9 degrees. The front foot catch phase peak impact VGRF was 3.4 ± 1.2 BW loading at a rate of 285 ±119 BW.s-1. The results indicate that although loading rates are not excessive during the catch phase, careful consideration should be given before introducing the jerk into the strength and conditioning program of the inexperienced

Practical applications of biomechanical principles in resistance training: The use of bands and chains

In recent years, it has become popular for athletes and recreational trainers to perform resistance training with the addition of bands and chains. In this paper, we consider the advantages of manipulating an exercise to match the resistance provided with the force capabilities of the lifter, which generally change throughout the movement. We explain that bands and chains can be used to manipulate a variety of exercises that have the potential to enhance performance in sport and in many daily tasks. Whilst there are many similarities between the use of bands and chains for resistance training, we note that there are key differences and discuss the biomechanics of each material separately. In particular, we discuss that chains provide resistance primarily in the vertical plane and the resistance is linearly related to the displacement of the barbell. In contrast, bands can be set up to produce substantial horizontal forces in addition to the primary resistance force that often acts in the vertical direction. Also, research has demonstrated that bands provide a resistance force that is related in a curvilinear fashion to the displacement of the barbell. After introducing the main biomechanical features associated with each type of resistance material, we present findings from the strength and conditioning literature that has demonstrated the potential for bands and chains to improve the stimulus associated with strength and power training. At present, a more compelling evidence base has emerged for the use of bands in resistance training, particularly with regard to the development of power. It is not known whether this asymmetry reflects the greater number of studies conducted with bands or is influenced by methodological differences between studies. However, we also discuss the possibility that different inertial properties of bands compared with chains may make the former a more effective choice for the development of power. We hope that exercise professionals will benefit from this knowledge and obtain insight into how an understanding of biomechanical principles can assist with prescribing contemporary training regimes

Practical applications of biomechanical principles in resistance training: moments and moment arms

Exercise professionals routinely prescribe resistance training to clients with varied goals. Therefore, they need to be able to modify the difficulty of a variety of exercises and to understand how such modifications can alter the relative joint loading on their clients so to maximise the potential for positive adaptation and to minimise injury risk. This paper is the first in a three part series that will examine how a variety of biomechanical principles and concepts have direct relevance to the prescription of resistance training for the general and athletic populations as well as for musculoskeletal injury rehabilitation. In this paper, we start by defining the terms moment (torque), moment arms, compressive, tensile and shear forces as well as joint stress (pressure). We then demonstrate how an understanding of moments and moment arms is integral to the exercise professionals’ ability to develop a systematic progression of variations of common exercises. In particular, we examine how a variety of factors including joint range of motion, body orientation, type of external loading, the lifter’s anthropometric proportions and the position of the external load will influence the difficulty of each exercise variation. We then highlight the primary results of several selected studies which have compared the resistance moment arms and joint moments, forces or stresses that are encountered during selected variations of common lower body resistance training exercises. We hope that exercise professionals will benefit from this knowledge of applied resistance training biomechanics and be better able to systematically progress exercise difficulty and to modify joint loading as a result. The two remaining articles in this series will focus on the neuromechanical properties of the human musculoskeletal system and better understanding the biomechanical implications of a variety of alternative resistance training techniques, respectively

Comparison of Different Minimal Velocity Thresholds to Establish Deadlift One Repetition Maximum

The aim of this study was to compare the actual deadlift one repetition maximum (1RM) and the deadlift 1RM predicted from individualised load-velocity profiles. Twelve moderately resistance-trained men participated in three deadlift sessions. During the first, 1RM was assessed; during the second, load-velocity profiles were recorded with six loads (65% to 90% 1RM) using a linear position transducer recording at 1000 Hz; and during the third, minimal velocity thresholds (MVT) were recorded from the velocity of the last repetition during sets to volitional fatigue with 70% and 80% 1RM with a linear position transducer recording at 1000 Hz. Regression was then used to generate individualised load-velocity profiles and the MVT was used as a cut-off value from which to predict deadlift 1RM. In general, velocity reliability was poor to moderate. More importantly, predicted deadlift 1RMs were significantly and meaningfully less than actual deadlift 1RMs (p < 0.05, d = 1.03–1.75). The main practical application that should be taken from the results of this study is that individualized load-velocity profiles should not be used to predict deadlift 1RM. Practitioners should not use this method in combination with the application of MVT obtained from the last repetition of sets to volitional fatigue

Wolf (Canis lupus) Winter Density and Territory Size in a Low Biomass Moose (Alces alces) System

We investigated the winter density and territory size of wolves (Canis lupus) on the Yukon Flats, Alaska, where moose (Alces alces) was the sole ungulate prey, occurring at a low density and representing a biomass of ungulate food lower than previously studied in North America. Using locations (GPS coordinates) from collars deployed on seven wolves, we estimated territory sizes with adaptive kernel and minimum convex polygon methods. We then estimated wolf density from a population area defined by these territory sizes and counts of wolves in five marked packs. From November 2009 to April 2010, we obtained 6263 GPS locations. Pack size ranged from two to 10 wolves, with average size of 5.0 in November 2009 and 4.8 in March 2010. Average winter territory size for five packs was 1433 km2 with the 95% adaptive kernel method and 1608 km2 with the minimum convex polygon method. Density (wolves/1000 km2) was 3.6 in November and 3.4 in March with the 95% adaptive kernel method and 3.4 in both November and March with the minimum convex polygon method. Territories were large and estimates produced by the two methods differed by 11%. Densities were low, and the two analysis methods yielded densities that differed from each other by 3% to 6%. Low wolf density corresponded with low biomass of ungulate food, suggesting that moose availability on the Yukon Flats likely limited wolf density.Nous avons étudié la densité hivernale et la taille du territoire du loup (Canis lupus) aux Yukon Flats, en Alaska, où l’orignal (Alces alces) était la seule proie ongulée. Il s’y trouvait en faible densité et représentait une biomasse de nourriture ongulée inférieure à celle étudiée ailleurs en Amérique du Nord. Grâce aux positions (coordonnées de GPS) prélevées à partir de colliers posés sur sept loups, nous avons estimé la taille des territoires au moyen de la méthode d’estimation adaptative à noyaux et de la méthode du polygone convexe minimal. Ensuite, nous avons estimé la densité du loup à partir d’une zone de population définie par la taille de ces territoires et par les dénombrements de loups de cinq meutes marquées. De novembre 2009 à avril 2010, nous avons obtenu 6 263 positions GPS. La taille des meutes variait de deux à dix loups, pour une taille moyenne de 5,0 loups en novembre 2009 et de 4,8 en mars 2010. La taille moyenne du territoire hivernal de cinq meutes était de 1 433 km2 dans le cas de la méthode adaptative à noyaux de 95 % et de 1 608 km2 dans le cas de la méthode du polygone convexe minimal. La densité (loups/1000 km2) était de 3,6 en novembre et de 3,4 en mars avec la méthode adaptative à noyaux de 95 % et de 3,4 en novembre et en mars avec la méthode du polygone convexe minimal. Les territoires étaient vastes et les estimations obtenues à l’aide des deux méthodes différaient de 11 %. Les densités étaient faibles, et les deux méthodes d’analyse ont donné des densités qui différaient l’une de l’autre dans une mesure 3 % à 6 %. La faible densité des loups correspondait à la faible biomasse de nourriture ongulée, ce qui laisse supposer que la disponibilité de l’orignal aux Yukon Flats limitait vraisemblablement la densité du loup

Practical applications of biomechanical principles in resistance training: Moments and moment arms

Exercise professionals routinely prescribe resistance training to clients with varied goals. Therefore, they need to be able to modify the difficulty of a variety of exercises and to understand how such modifications can alter the relative joint loading on their clients so to maximise the potential for positive adaptation and to minimise injury risk. This paper is the first in a three part series that will examine how a variety of biomechanical principles and concepts have direct relevance to the prescription of resistance training for the general and athletic populations as well as for musculoskeletal injury rehabilitation. In this paper, we start by defining the terms moment (torque), moment arms, compressive, tensile and shear forces as well as joint stress (pressure). We then demonstrate how an understanding of moments and moment arms is integral to the exercise professionals’ ability to develop a systematic progression of variations of common exercises. In particular, we examine how a variety of factors including joint range of motion, body orientation, type of external loading, the lifter’s anthropometric proportions and the position of the external load will influence the difficulty of each exercise variation. We then highlight the primary results of several selected studies which have compared the resistance moment arms and joint moments, forces or stresses that are encountered during selected variations of common lower body resistance training exercises. We hope that exercise professionals will benefit from this knowledge of applied resistance training biomechanics and be better able to systematically progress exercise difficulty and to modify joint loading as a result. The two remaining articles in this series will focus on the neuromechanical properties of the human musculoskeletal system and better understanding the biomechanical implications of a variety of alternative resistance training techniques, respectively

Practical applications of biomechanical principles in resistance training: Neuromuscular factors and relationships

This paper is the second in our three part series examining how a variety of biomechanical principles and concepts\ud have direct relevance to the prescription of resistance training for the general and athletic populations as well as for\ud musculoskeletal injury rehabilitation. In this paper, we considered different neuromuscular characteristics of resistance\ud exercise. We started by defining the causes of motion, discussing force and Newton’s second law of linear motion. This\ud led to discussion of impulse, and how its relationship with momentum can be used to study force-time curves recorded\ud from different ground-based resistance exercises. This enables the sports biomechanist to derive movement velocity,\ud which enables study of the relationship between force and velocity, and we concluded that as the force required to\ud cause movement increases the velocity of movement must decrease. This relationship is critical because it enables\ud strength and conditioning coaches and exercise professionals to manipulate resistance-training loads to maximise\ud training gains for sports performance. We described representative force-time curves from basic human movements\ud to provide a foundation for discussion about how different resistance-training gains can be achieved. This focused on\ud exercise technique, including use of the stretch-shortening cycle, magnitude of load, ballistic resistance exercise, and\ud elastic band and chain resistance (although elements of this will receive greater attention in our final article). Finally, we\ud defined and explained the concept of mechanical work and power output, examining the effect that load has on power\ud output by considering the load-power relationships of different common resistance exercises. We hope that exercise\ud professionals will benefit from this knowledge of applied resistance training biomechanics. Specifically, we feel that\ud the take home message of this article is that resistance exercise load and technique can be manipulated to maximise\ud resistance-training gains, and that this can be particularly useful for athletes trying to improve sporting performance

Do the peak and mean force methods of assessing vertical jump force asymmetry agree?

The aim of this study was to assess agreement between peak and mean force methods of quantifying force asymmetry during the countermovement jump (CMJ). Forty-five men performed four CMJ with each foot on one of two force plates recording at 1000 Hz. Peak and mean were obtained from both sides during the braking and propulsion phases. The dominant side was obtained for the braking and propulsion phase as the side with the largest peak or mean force and agreement was assessed using percentage agreement and the kappa coefficient. Braking phase peak and mean force methods demonstrated a percentage agreement of 84% and a kappa value of 0.67 (95% confidence limits: 0.45 to 0.90), indicating substantial agreement. Propulsion phase peak and mean force methods demonstrated a percentage agreement of 87% and a kappa value of 0.72 (95% confidence limits: 0.51 to 0.93), indicating substantial agreement. While agreement was substantial, side-to-side differences were not reflected equally when peak and mean force methods of assessing CMJ asymmetry were used. These methods should not be used interchangeably, but rather a combined approach should be used where practitioners consider both peak and mean force to obtain the fullest picture of athlete asymmetry