Authors: Dimitrije Cabarkapa 1, Andrew C. Fry 1, and Eric M. Mosier 2
1Jayhawk Athletic Performance Laboratory, University of Kansas, Lawrence, KS, USA
2 Northwest Missouri State University, Maryville, MO, USA
Dimitrije Cabarkapa, MS, CSCS, NSCA-CPT, USAW
Jayhawk Athletic Performance Laboratory
University of Kansas
1301 Sunnyside Avenue, Lawrence, KS 66047
Kinetics and Kinematics of Commonly Used Quarterback Throwing Approaches – A Case Study
The purpose of this study was to analyze kinetic and kinematic components for six of the most commonly used quarterback drop throwing patterns and determine how further performance improvements can be made. One male right-handed quarterback athlete volunteered to perform multiple repetitions of the six most commonly used right-handed drop throwing approaches: standing still and throw (SST), one-step left-right (1SLR), one-step right-left (1SRL), three-step straight ahead (3SSA), three-step shot gun (3SSG), and five-step throw (5ST). Kinetic data was collected with a uniaxial force plate while kinematic data was captured with high definition cameras. One-way analysis of variance was used to determine the differences between the six throwing approaches for the kinetic and kinematic variables examined in this study. The statistical significance level was set a priori to p<0.05. Peak right leg force demonstrated significantly lower magnitudes for 1SRL when compared to 1SLR, 3SSG, and 5ST. Peak left leg force for the 3SSA was lower when compared to 1SRL and 1SLR. Throw arm elbow angle was greater for SST when compared to all other throwing approaches. No difference was observed for ball speed, non-throw arm elbow angle, front leg knee angle, and back leg knee angle between any of the examined throwing approaches. Our results indicate that the majority of ground reaction force production required for an optimal quarterback throwing motion comes from the rear leg, and the magnitudes may reach three times bodyweight forces. Ground reaction forces may be enhanced with a greater number of drop steps, which may ultimately increase quarterback throwing distance. Greater throwing arm elbow extension may be induced as biomechanical adjustment due to lack of force production caused by the inability of the quarterback to take a greater number of drop steps.
Key Words: sport performance, American football, force, resistance training
The quarterback position in American football plays a major role in the overall team success and the level of their performance can potentially determine the final game outcome. Despite the popularity of this sport, there is a lack of scientific literature on addressing the fundamental kinetic and kinematic components of commonly utilized quarterback throwing approaches to help determine how performance improvements can be made. While the majority of sports that involve ball throwing motions such as team handball, baseball, softball, and football have similar throwing fundamentals, certain critical differences in their biomechanical characteristics exist. Handball throwing motion was found to be analogous to football throwing motion except for a greater humeral rotation (4). Baseball pitching demonstrated a greater and earlier occurrence of upper torso rotation, elbow extension, and shoulder internal rotation when compared to a standard quarterback throwing motion (3).
It has been suggested that periodized resistance training focused on the implementation of multi-joint exercises and multiple exercise sets can improve quarterback throwing performance through muscular strength, power, and endurance development (9). Football players that participated in resistance training programs successfully improved bench strength and leg press performance (8). Considering that the quarterback throwing motion requires full-body motion involvement, we may assume that these physiological improvements would ultimately lead to throwing performance enhancement. While no research studies examined the influence of resistance training programs on quarterback throwing performance to our knowledge, Young et al. found a positive relationship between football kicking performance and individual player strength development (10). Even though strength and power development may be one of the critical factors for athletes’ development, we need to be aware of individual differences and specific playing position requirements. To appropriately prescribe and design resistance training programs, coaches should be aware of the biomechanical characteristics of various sport-specific motions and the physiological requirements of each playing position (8), which would ultimately lead to the development of optimal individually tailored resistance training programs and provide quarterbacks with an opportunity to improve their throwing performance.
Thus, the purpose of this case study was to analyze kinetic and kinematic components for six of the most commonly used quarterback drop throwing patterns, and to provide coaches and strength and conditioning professionals with essential information to help optimize resistance training program development which can ultimately lead to improvements in in-game quarterback throwing performance.
One male right-handed quarterback athlete (height = 188 cm, weight = 95.2 kg, age = 20 years) competing at the National Collegiate Athletic Association (NCAA) Division-I level of competition volunteered to participate in this research study. Before any testing procedures were conducted, the subject signed an informed consent form. All testing procedures were previously approved by the University’s Institutional Review Board committee.
Upon arrival at the testing facility the subject was familiarized with the testing equipment and procedures. The subject was asked to completed a standardized warm-up consisting of a 5-minute treadmill run at a moderate intensity, and a set of dynamic warm-up motions such as high knees, butt-kicks, lunge-and-twist, knee to chest, high skips, lateral slides, tuck jumps, A-skips, and forward lunges. After the warm-up completion, the subject performed multiple repetitions of the six most commonly used right-handed drop throwing approaches: standing still and throw (SST), one-step left-right (1SLR), one-step right-left (1SRL), three-step straight ahead (3SSA), three-step shot gun (3SSG), and five-step throw (5ST). Considering that the subject was right hand dominant, the rear leg was the right leg, while the front leg was the left leg. The graphical representation of the six quarterback throwing approaches examined in this study is presented in Figure 1.
A 0.91 m x 2.4 m (3’ x 8’) uniaxial force plate (Rice Lake Weighing Systems, Rice Lake, WI) and data acquisition system (BioPac MP 150, Goleta, CA) sampling at 1000 Hz was used for kinetic data collection. Example of the ground reaction force curve is presented in Figure 2. Kinematic data was captured with high definition cameras (Canon SX530 PowerShot and Casio Exilim EX-ZR100) sampling at 30 Hz and analyzed with Kinovea Version 0.8.24 video analysis software. A speed radar (Country Technology, Gray Mills, WI) was used to capture the velocity of each football throw. For each throwing approach, all the devices recorded the data simultaneously. Footballs used in this study corresponded to the official game regulation size. A 15 cm stationary throwing target was positioned approximately 15 meters (16.4 yds) away from the subject’s throwing site, and it stayed constant for all of the throwing approaches examined in this study. The complete experimental set-up is shown in Figure 3.
Peak right (rear) and left (front) leg forces were determined as the highest point on the ground reaction force curve during the concentric phase of the throwing motion. Ball times were determined from video analysis as the time from the initial body movement to the time-point of the ball release. Throw velocities are reported as the value in miles per hour (mph) displayed on the radar gun. Throwing times were determined from the initiation of the quarterback drop step to the time point of the ball release. Front and back leg knee angle variables represent the internal angle formed between the thigh and shank segments with the fulcrum located at the center of the knee joint (Figure 4). In a similar manner, both throw arm and non-throw arm elbow angle capture the internal angle between arm and forearm arm with the fulcrum located at the center of the elbow joint (Figure 4). All of the previously mentioned kinematic variables regarding the upper and lower body limb positioning have been computed during the cocking phase at the initial point of the forward arm throwing motion.
Descriptive statistics and standard deviations (x̄±SD) were calculated for each of the dependent variables. One-way analysis of variance (ANOVA) with Bonferroni adjustments for the Post Hoc comparisons were used to analyze the data to determine the differences between kinetic and kinematic variables examined in this study. Levene’s test was used to test for the homogeneity of variance and did not reach statistical significance for any of the examined variables. The statistical significance level was set a priori to p<0.05. All statistical analyses were computed with the SPSS Version 25.0 software (SPSS Inc. Chicago, IL, USA).
Mean values and standard deviations (x̄±SD) for each of the dependent variables examined in this study are presented in Tables 1 and 2. The ball release time was significantly different between each of the examined approaches (p<0.001), except no difference was observed between 1SRL and 1SLR (p>0.05). Peak left leg force for the 3SSA throwing approach was significantly lower when compared to 1SRL (p=0.001) and 1SLR (p=0.002). Peak right leg force demonstrated significantly lower magnitudes for 1SRL throwing approach when compared to 1SLR (p=0.004), 3SSG (p=0.001), and 5ST (p=0.012), while 3SSA approach was significantly different when compared to 1SLR (p=0.008), 3SSG (0.003), and 5ST (p=0.025). Throw arm elbow angle was greater for SST throwing approach when compared to 1SRL (p<0.001), 1SLR (p<0.001), 3SSA (p=0.001), 3SSG (p=0.008), and 5ST (p<0.001). Additionally, the magnitudes for the throw arm elbow angle were significantly lower for 1SLR throwing approach when compared to SST (p<0.001), 3SSA (p=0.021), 3SSG (p=0.002), and 5ST (p=0.033), while no difference was observed when compared to 1SRL (p>0.05). No difference was observed for ball speed, non-throw arm elbow angle, front leg knee angle, and back leg knee angle between any of the examined throwing approaches (p>0.05).
Table 1. Kinetic, velocity, and timing variables for the examined quarterback throwing approaches. Standing still and throw (SST), one-step right left (1SRL), one-step left right (1SLR), three-step straight ahead (3SSA), three-step shot gun (3SSG), five-step throw (5ST).
|Peak Force Front/Left Leg (N)||Peak Force Rear/Right Leg (N)||Ball Speed (mph / m•s-1)||Ball Release Time (sec)|
|SST||1185.2 ± 150.8||1443.9 ± 17.8||49.3 ± 1.5 / 22.0 ± 0.7||0.82 ± 0.05|
|1SRL||1370.9 ± 49.5 b||1340.4 ± 34.8 c||48.3 ± 1.5 / 21.6 ± 0.7||1.35 ± 0.02 a|
|1SLR||1352.1 ± 69.4 b||1490.8 ± 11.4||48.7 ± 1.2 / 21.8 ± 0.5||1.29 ± 0.02|
|3SSA||1024.8 ± 29.1||1352.9 ± 24.8 c||48.0 ± 1.0 / 21.5 ± 0.4||2.03 ± 0.00|
|3SSG||1207.8 ± 27.4||1471.8 ± 45.5||51.0 ± 1.0 / 22.8 ± 0.4||2.25 ± 0.05|
|5ST||1197.4 ± 30.8||1510.2 ± 59.2||49.7 ± 0.6 / 22.2 ± 0.3||2.61 ± 0.09|
a – no difference when compared to 1SLR (p>0.05)
b – greater than 3SSA (p<0.05)
c – lower than 1SLR, 3SSG, 5ST (p<0.05)
Table 2. Kinematic variables for the examined quarterback throwing approaches. Standing still and throw (SST), one-step right left (1SRL), one-step left right (1SLR), three-step straight ahead (3SSA), three-step shot gun (3SSG), five-step throw (5ST).
|Front/Left Leg Knee Angle (deg)||Rear/Right Leg Knee Angle (deg)||Throw Arm Elbow Angle (deg)||Non-Throw Arm Elbow Angle (deg)|
|SST||138.7 ± 1.2||129.7 ± 4.2||93.7 ± 1.5 a||30.0 ± 3.6|
|1SRL||136.0 ± 2.0||128.7 ± 0.6||83.3 ± 1.5||36.3 ± 1.5|
|1SLR||138.0 ± 2.0||130.0 ± 3.0||80.3 ± 2.5 b||35.3 ± 2.5|
|3SSA||134.3 ± 2.1||128.3 ± 2.1||85.7 ± 0.6||33.7 ± 4.5|
|3SSG||135.0 ± 1.0||130.3 ± 2.1||87.7 ± 1.2||30.5 ± 2.5|
|5ST||137.3 ± 1.2||124.3 ± 1.5||85.3 ± 1.5||30.0 ± 1.0|
a – greater than all others (p<0.05)b – lower than all others (p<0.05), except 1SRL
Based on our findings, peak ground reaction forces for the rear/right leg were noticeably greater when compared to the front/left leg. When reflecting on the nature of American football, quarterbacks are required to achieve an optimal throwing motion within a minimal amount of time while under a considerable amount of pressure (7). Considering the stride length and time frame that the quarterback has to release the ball, we can assume this necessitates relying on the rear foot for force production in order to achieve an optimal throwing motion. Our findings differ from ground reaction forces observed within a cohort of collegiate and high-school baseball pitchers where the greatest levels of vertical forces were observed for the stride limb (front leg) with magnitudes approximately double the bodyweight forces (5). It should also be noted that for athletes in both sports, these forces are expressed through just a single lower limb. This difference may be mainly caused by a greater stride length and time allowed for completion of this body motion. Moreover, it seems that the larger the number of drop steps the quarterback takes, the greater the rear foot ground reaction forces. The vertical rear foot forces were up to three times greater than the quarterback body weight, which may ultimately lead to an increase in throwing distances. Although not evident in these data, it is likely to be apparent when making realistic throws on an actual field.
While the contribution of the lower body to the proper execution of a football throwing motion is undisputed, Fleisig and colleagues indicated that a considerable amount of force production results from elbow and shoulder joint flexion (2). Despite the presence of a certain degree of video distortion when analyzing the non-throw arm elbow angle due to the sagittal view camera placement, the conclusions from the kinematic data analysis for the elbow were not likely affected. Our findings reveal no difference in non-throw arm elbow angle, front leg knee angle, and back leg knee angle between any of the throwing approaches examined in this study. However, the SST throwing arm elbow magnitudes were significantly greater when compared to the rest of the throwing approaches. Previous research indicates that an athlete’s ability to achieve proper joint alignment and optimal eccentric muscle forces during the cocking phase of the throwing motion can augment the concentric phase of the motion (2,9). Thus, the smaller elbow flexion observed for the SST approach might be initiated by biomechanical adjustments necessary to make up for the lack of force production caused by the quarterback’s inability to take one or more penultimate steps such as observed in the one, three, and five-step throwing approaches. Another important factor that needs to be considered is the amount of time required for completion of the throwing motion. While no differences in ball throwing velocities were detected, our findings indicate significant differences in the drop step and throwing motion times between all of the examined approaches except between 1SLR and 1SRL. The SST approach might be a beneficial method for a quick ball release required in the close presence of the defensive player or during execution of a special play. However, it has been suggested that quick strides and an insufficient amount of time may negatively impact an optimal sequence of the preparatory throwing motions (9). These factors can potentially elicit a negative effect on kinetic chaining synchronization (optimal contraction sequence of neighboring joints and segments) and ultimately impair throwing performance (2,9). Hence, we may assume that the greatest rear leg forces observed for the 5ST throwing approach may be induced by a greater amount of time for preparation and kinetic chain synchronization, which in a practical setting may be able to augment throwing performance.
Having a basic understanding of the kinetic and kinematic characteristics of the most utilized quarterback throwing approaches may help athletic trainers and strength and conditioning professionals enhance on-field performance and minimize risk of non-contact injuries. Previous research found that quarterbacks have five times greater chances of injury when compared to the offensive lineman and linebacker playing positions, with the most injured sites being the knee, wrist, and ankle joints (1). Kelly and colleagues’ findings further support the vulnerability of the quarterback position indicating that 15% of injuries were non-contact in nature, and reveal that along with shoulder injuries, were the top two injuries (6). Considering the significant amount of ground reaction force initiated by the lower body and successively transmitted through motion kinetic chaining affecting the ankle, knee, hip, shoulder, elbow, and wrist joints, we may assume that our findings agree with previous literature and that emphasizes the importance of properly designed and implemented resistance training programs. Additionally, further research should consider utilizing three-dimensional markerless motion tracking systems to optimize kinetic and kinematic data collection and decrease a margin of error that may be attributed by a certain degree of video distortion.
The majority of ground reaction force production required for an optimal quarterback throwing motion comes from the rear leg, and the magnitudes may reach three times bodyweight forces. Ground reaction forces may be enhanced with a greater number of drop steps, which may ultimately increase quarterback throwing distance. Greater throwing arm elbow extension may be induced as biomechanical adjustment due to lack of force production caused by the inability of the quarterback to take a greater number of drop steps.
APPLICATIONS IN SPORT
This data can be used by strength and conditioning professionals to obtain a better insight into quarterback kinetic and kinematic throwing performance requirements and serve as a guideline for optimal choice of resistance training exercises, especially considering that peak ground reaction forces can reach a magnitude of approximately three times subject’s body weight. Properly designed and well-implemented strength and conditioning programs may further improve quarterback throwing performance and aid in the prevention of non-contact injuries.
This investigation was supported through an award from the University of Kansas School of Education Student Research Fund. The authors thank the participant for volunteering to complete the testing protocols in this study.
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