Shop NASE

Abstract: A novel approach of analyzing complete ground reaction force waveforms rather than discrete kinetic variables can provide new insight to sprint biomechanics. This study aimed to understand how these waveforms are associated with better performance across entire sprint accelerations. Twenty‐eight male track and field athletes (100‐m personal best times: 10.88 to 11.96 seconds) volunteered to participate. Ground reaction forces produced across 24 steps were captured during repeated (two to five) maximal‐effort sprints utilizing a 54‐force‐plate system. Force data (antero‐posterior, vertical, resultant, and ratio of forces) across each contact were registered to 100% of stance and averaged for each athlete. Statistical parametric mapping (linear regression) revealed specific phases of stance where force was associated with average horizontal external power produced during that contact. Initially, antero‐posterior force production during mid‐late propulsion (eg, 58%‐92% of stance for the second ground contact) was positively associated with average horizontal external power. As athletes progressed through acceleration, this positive association with performance shifted toward the earlier phases of contact (eg, 55%‐80% of stance for the eighth and 19%‐64% for the 19th ground contact). Consequently, as athletes approached maximum velocity, better athletes were more capable of attenuating the braking forces, especially in the latter parts of the eccentric phase. These unique findings demonstrate a shift in the performance determinants of acceleration from higher concentric propulsion to lower eccentric braking forces as velocity increases. This highlights the broad kinetic requirements of sprinting and the conceivable need for athletes to target improvements in different phases separately with demand‐specific exercises.
Reference
S.L. Colver, R. Nagahara, and A.I. T. Salo. 2018. Kinetic demands of sprinting shift across the acceleration phase: Novel analysis of entire force waveforms. Scandinavian Journal of Medicine and Science in Sports. 06 April 2018 https://doi.org/10.1111/sms.13093

Abstract
Backward running (BR) is a form of locomotion that occurs in short bursts during many overground field and court sports. It has also traditionally been used in clinical settings as a method to rehabilitate lower body injuries. Comparisons between BR and forward running (FR) have led to the discovery that both may be generated by the same neural circuitry. Comparisons of the acute responses to FR reveal that BR is characterized by a smaller ratio of braking to propulsive forces, increased step frequency, decreased step length, increased muscle activity and reliance on isometric and concentric muscle actions. These biomechanical differences have been critical in informing recent scientific explorations which have discovered that BR can be used as a method for reducing injury and improving a variety of physical attributes deemed advantageous to sports performance. This includes improved lower body strength and power, decreased injury prevalence and improvements in change of direction performance following BR training. The current findings from research help improve our understanding of BR biomechanics and provide evidence which supports BR as a useful method to improve athlete performance. However, further acute and longitudinal research is needed to better understand the utility of BR in athletic performance programs.

Coaching Implications
Performance in numerous sports such as football, basketball, soccer, field hockey, rugby, lacrosse, tennis and others can be enhanced by incorporating backward sprinting into the regular training sessions both in-season and off-season. Although backward sprinting for short distances is commonly required in various sports, training to improve movement efficiency and the speed-strength of the specific muscles involved is quite uncommon. 
ReferenceAaron Uthoff, Jon Oliver, John Cronin, Craig Harrison and Paul Winwood. 2018. A New Direction to Athletic Performance: Understanding the Acute and Longitudinal Responses to Backward Running. Sports Medicine May 2018, Volume 48, Issue 5, pp 1083–1096.

This study provides new information concerning specific training exercises that elicit a higher vertically-directed ground reaction force (GRF); a key factor in determining maximum mph speed.

Abstract

External load training (ELT) is a supplemental training method used to potentially improve high intensity task performance. However, biomechanical parameters such as ground reaction forces (GRF), ground contact time, and time to peak GRF during a drop vertical jump (DVJ) following an ELT intervention have yet to be examined. Therefore, this study investigated the impact of ELT on certain biomechanical parameters of a DVJ task. Well-trained females stratified into two groups (ELT = 9, Control = 10) completed a DVJ from a 45.72 cm box onto a force platform at baseline, post-ELT, and post-detraining (DET). ELT consisted of wearing weight vests (WV) with 8% body mass for 32 h/week during daily living and 3 training sessions/week for 3 weeks. After ELT, a 3 week DET phase was completed. The control group replicated procedures without ELT intervention. The vertical, medial/lateral, and anterior/posterior components of the GRF were assessed during the initial contact, minimum force following initial contact, push-off, and second landing periods. Dependent variables were analyzed using a 2 (group) × 3 (time) mixed model ANOVA (p < .05). Significantly greater peak vertical GRF during the initial contact period was identified for the ELT group. Significant increases in the minimum vertical GRF following the initial contact period from baseline to post-ELT following the were observed for the ELT group, while significant increases in peak vertical GRF during the second landing period at post-ELT and post-DET in comparison to baseline was observed for both groups. The combination of greater vertical GRF during the initial contact period and the period following initial contact suggests that ELT may increase GRFs during a DVJ in comparison to routine training without a weighted vest.

Coaching Application

The drop vertical jump exercise should be a regular part of a training program to increase vertically-directed ground reaction force and the maximum speed phase of a sprint.

Reference

Jeffrey D. Simpson, Brandon L. Miller, Erik K. O”Neal, Harish Chandlerr and Adam C. Knight. 2018. Ground reaction forces during a drop vertical jump: Impact of external load training.Human Movement Science Volume 59, June 2018, Pages 12-19

Abstract

This cross-sectional study aimed to investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development: RTD) versus sprint performance in elite youth football players.

Methods:

Thirty elite academy youth football players (16.75 ± 1.1 years, 176.9 ± 6.7 cm, 67.1 ± 6.9 kg) were included. Isometric peak torque (Nm/kg) and early (0-100 ms) and late (0-200 ms) phase RTD (RTD100, RTD200) (Nm/s/kg) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m sprint trial. Mechanical sprint variables (maximal horizontal force production (FH0) (N/kg); maximal theoretical velocity (V0) (m/s); maximal horizontal power output (Pmax) (W/kg)) and sprint split times (0-5 m; 0-15 m; 0-30 m; 15-30 m) (s) were derived as dependent variables. Subsequently, linear regression analysis was conducted for each pair of dependent and independent variables.

Results:

Positive associations were observed between hamstring RTD100 and FH0 (r2=0.241, p=0.006) and Pmax (r2=0.227, p=0.008). Furthermore, negative associations were observed between hamstring RTD100 and 0-5 m (r2=0.206, p=0.012), 0-15 m (r2=0.217, p=0.009) and 0-30 m sprint time (r2=0.169, p=0.024). No other associations were observed.

Conclusion:

The present data indicate that early-phase (0-100 ms) rapid force capacity of the hamstring muscles plays an important role for the acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity.

Coaching Application:

Strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.

Reference

Lassee Ishol, Per Aagaard, Mathias F. Nielsen, Kasper B. Thorton. 2018. The Influence of Hamstring Muscle Peak Torque and Rate Of Torque Development for Sprinting Performance in Football Players: A Cross-Sectional Study. Human Kinetics, Volume:0 Issue: 0 Pages:1-27 doi: 10.1123/ijspp.2018-0464

Abstract:

The purpose of this study was to determine the braking and propulsive phase kinetic variables underpinning reactive strength in highly trained sprint athletes in comparison with a nonsprint-trained control group. Twelve highly trained sprint athletes and 12 nonsprint–trained participants performed drop jumps (DJs) from 0.25, 0.50, and 0.75 m onto a force plate. One familiarization session was followed by an experimental testing session within the same week. Reactive strength index (RSI), contact time, flight time, and leg stiffness were determined. Kinetic variables including force, power, and impulse were assessed within the braking and propulsive phases. Sprint-trained athletes demonstrated higher RSI vs. nonsprint–trained participants across all drop heights {3.02 vs. 2.02; ES (±90% confidence limit [CL]): 3.11 ± 0.86}. This difference was primarily attained by briefer contact times (0.16 vs. 0.22 seconds; effect size [ES]: −1.49 ± 0.53) with smaller differences observed for flight time (0.50 vs. 0.46 seconds; ES: 0.53 ± 0.58). Leg stiffness, braking and propulsive phase force, and power were higher in sprint-trained athletes. Very large differences were observed in mean braking force (51 vs. 38 N·kg−1; ES: 2.57 ± 0.73) which was closely associated with contact time (r ±90% CL: −0.93 ± 0.05). Sprint-trained athletes exhibited superior reactive strength than nonsprint–trained participants. This was due to the ability to strike the ground with a stiffer leg spring, an enhanced expression of braking force, and possibly an increased utilization of elastic structures. The DJ kinetic analysis provides additional insight into the determinants of reactive strength which may inform subsequent testing and training.

Coaching Application

This study reinforces the importance of various training techniques to improve ground reaction force – the force applied the after the foot strikes the ground each stride during the start, acceleration, and maximum speed phase of a short sprint. In addition, leg stiffness at ground contact and braking and propulsive force are higher in trained sprinters indicating the value of proper sprint mechanics and speed strength training.

Reference

Douglas, J, Pearson, S, Ross, A, and McGuigan, M. Kinetic determinants of reactive strength in highly trained sprint athletes. J Strength Cond Res 32(6): 1562–1570, 2018

Abstract The study sheds some light on how correct training can allow athletes to continue accelerting anf atttain a higher maximum speed. Forces applied to the ground during sprinting are vital to performance. This study aimed to understand how specific aspects of ground reaction force waveforms allow some individuals to continue to accelerate beyond the velocity plateau of others. Twenty‐eight male sprint specialists and 24 male soccer players performed maximal‐effort 60‐m sprints. A 54‐force‐plate system captured ground reaction forces, which were used to calculate horizontal velocity profiles. Touchdown velocities of steps were matched (8.00, 8.25, and 8.50 m/s), and the subsequent ground contact forces were analyzed. Mean forces were compared across groups and statistical parametric mapping (t tests) assessed for differences between entire force waveforms. When individuals contacted the ground with matched horizontal velocity, ground contact durations were similar. Despite this, sprinters produced higher average horizontal power (15.7‐17.9 W/kg) than the soccer players (7.9‐11.9 W/kg). Force waveforms did not differ in the initial braking phase (0%‐~20% of stance). However, sprinters attenuated eccentric force more in the late braking phase and produced a higher antero‐posterior component of force across the majority of the propulsive phase, for example, from 31%‐82% and 92%‐100% of stance at 8.5 m/s. At this velocity, resultant forces were also higher (33%‐83% and 86%‐100% of stance) and the force vector was more horizontally orientated (30%‐60% and 95%‐98% of stance) in the sprinters. These findings illustrate the mechanisms which allowed the sprinters to continue accelerating beyond the soccer players’ velocity plateau. Moreover, these force production demands provide new insight regarding athletes’ strength and technique training requirements to improve acceleration at high velocity.

Reference

Steffi L. Colyer, Ryu Nagahara, and Yohei Takai. 2018. How sprinters accelerate beyond the velocity plateau of soccer players: Waveform analysis of ground reaction forces. Scandinavian Journal of Medicine & Science in Sports 19 September 2018 https://doi.org/10.1111/sms.13302

The study reinforces the importance of ground reaction force GRF) and describes how athletes are able to apply greater amounts of mass-specific force to the ground in the shortest possible time.

Abstract

Sprint running performance can be investigated relatively simply at the whole-body level by examining the timing of the phases of the stride and the forces applied to the ground in relation to a runners body weight. Research using this approach has been used to address a number of basic questions regarding the limits and determinants of human running speed. The primary differentiating factor for the top speeds of human runners is how forcefully they can strike the ground in relation to body mass. A general relationship between mass-specific force application and maximum running speeds results from the similar durations of the aerial and swing phases of the stride for different runners. Recent work has elucidated the mechanism by which faster runners are able to apply greater mass-specific ground forces in the very brief foot-ground contact times sprinting requires.

Coaching Application

The amount of force an athlete can apply to the ground in relation to body weight and the speed with which the force can be applied (ground contact time) is a key factor in improving speed during each of the four phases of a short sprint (the start, acceleration, maximum speed, and deceleration phase). Both the amount of force production and the speed of force application can be improved with proper training.

Reference

Weyand, Peter (2017) “FORCE, MOTION, SPEED: A GROUNDED PERSPECTIVE ON HUMAN RUNNING PERFORMANCE,” ISBS Proceedings Archive: Vol. 35 : Iss. 1 , Article 289. Available at: https://commons.nmu.edu/isbs/vol35/iss1/289

This study takes a careful look at how a season of football affects the general health of Division I players.

Abstract
Among high school and collegiate football players, research shows that 56% of football players are considered obese. Training during a season involves rigorous cardio and strength conditioning to physically prepare for the necessary sport skills. While a preseason physical exam is required, minimal health information is gathered post season.

PURPOSE: The purpose of this pilot study was to compare health markers during a pre and post collegiate football season among Division 1 football players.

METHODS: Eleven male freshman players (18±0.24 years) volunteered to be tested before the start of the competitive season. Testing for health markers included demographics (age, height, and weight), fasting Low Density Lipoprotein (LDL), High Density Lipoprotein (HDL), blood glucose (BG), blood pressure (BP), and triglycerides (TRI). Body Mass Index (BMI) was calculated and additional measures included percent body fat (%BF) and subcutaneous (SCAT) and visceral fat (VAT) depths. Players were reassessed at the end of the football season. Descriptive statistics and comparison between pre and post season were analyzed in SPSS (v24). A repeated measures ANOVA was conducted to compare health markers; alpha level was set at 0.05.

RESULTS: Ten out of the 11 subjects had a significant decrease in their systolic BP (pre: 131±6 mmHg, post: 118±7 mmHg; p=.001) and TRI (pre: 168.27±42.28 mg/dL, post: 116.82±42.28 mg/dL;p=.025). All other health markers had no significant change.

CONCLUSION: This data suggests that there has been a significant change from pre to post season in certain health markers related to cardiovascular health. This study opens the discussion of appropriate fitness training among football players beginning at an early stage. Does the training overlook the athlete’s health in preparation for the sport? This data also highlights the importance of dietary education for the players, as well as, requiring additional health assessments during a preseason physical exam. Further research on dietary consumption during a season is necessary to understand the impact of nutrition on the athlete’s health and fitness.

Coaching Application

Although findings were mostly favorable, the study highlights the need for improved in-
season nutritional guidance and perhaps more in-season fitness attention to cardiovascular health

Reference

Swanson, C; Vahk, A; Babcock, G; and Repovich, FACSM, W (2018) “HEALTH MARKERS IN DIVISION 1 FOOTBALL PLAYERS COMPARED PRE- TO POST-SEASON: A PILOT STUDY,” International Journal of Exercise Science: Conference Proceedings: Vol. 8 : Iss. 6 , Article 52. Available at: https://digitalcommons.wku.edu/ijesab/vol8/iss6/52

Injuries to the ankle and knee are common in the sport of basketball for both boys and girls. The study below compares the type and frequency of injuries between both genders.
Abstract

This prospective study investigated the incidence and pattern of acute time‐loss injuries in young female and male basketball players. Eight basketball teams (n=201; mean age 14.85±1.5) participated in the follow‐up study (2011‐2014). The coaches recorded player participation in practices and games on a team diary. A study physician contacted the teams once a week to check new injuries and interviewed the injured players. In total, 158 injuries occurred. The overall rate of injury (per 1000 hours) was 2.64 (95% CI 2.23‐3.05). Injury rate was 34.47 (95% CI 26.59‐42.34) in basketball games and 1.51 (95% CI 1.19‐1.82) in team practices. Incidence rate ratio (IRR) between game and practice was 22.87 (95% CI 16.71‐31.29). Seventy‐eight percent of the injuries affected the lower limbs. The ankle (48%) and knee (15%) were the most commonly injured body sites. The majority of injuries involved joint or ligaments (67%). Twenty‐three percent of the injuries were severe causing more than 28 days abseThe numberom sports. Number of recurrent injuries was high (28% of all injuries), and most of them were ankle sprains (35 of 44, 79%). No significant differences were found in injury rates between females and males during games (IRR 0.88, 0.55, to 1.40) and practices (IRR 1.06, 0.69, to 1.62). In conclusion, ankle and knee ligament injuries were the most common injuries in this study. Moreover, the rate of recurrent ankle sprains was alarming.

Coaching Application

Coaches could benefit by consulting athletic trainers concerning ankle injury prevention modalities that favorably reduce the incidence of initial and reoccurring injuries that are likely to result in lost practice and game time. Reseaerch indicates that prophylactic programs effectively reduce the risk of general lower extremity injuries and ankle sprains.

Reference

K. Pasanen, T. Ekola, T. Vasankai, P. Kannus, A. Heinonen, U.M. Kujala, and J. Parkari. 2016. High ankle injury rate in adolescent basketball: A 3‐year prospective follow‐up study. Scandinavian Journal of Medicine and Science in Sports Vol. 27, Issue 6.

The warm-up period prior to competition is often loosely and routinely completed with the dual purposes of preparing the body for more vigorous activity and decreasing the chance of soft tissue injury. The study described in the abstract below added a third dimension of possible performance enhancement by utilizing 3 depth jumps one minute after the dynamic stretching exercises to determine the immediate effect on 20-meter sprint performance.

Abstract

The purpose of this investigation was to determine whether the addition of 3 depth jumps to a dynamic warm-up (DYNDJ) protocol would significantly improve 20-m sprint performance when compared with a cardiovascular (C) warm-up protocol or a dynamic (DYN) stretching protocol alone. The first part of the study identified optimal drop height for all subjects using the maximum jump height method. The identified optimal drop heights were later used during the DYNDJ protocol. The second part compared the 3 warm-up protocols above to determine their effect on 20-m sprint performance. Twenty-nine subjects (age, 20.8 6 4.4 years; weight, 82.6 6 9.9 kg; height, 180.3 6 6.2 cm) performed 3 protocols of a C protocol, a DYN protocol, and a DYNDJ protocol in a randomized order. A 20-m sprint was performed 1 minute after the completion of each of the 3 protocols. Results displayed significant differences between each of the 3 protocols. A significant improvement (p = 0.001) of 2.2% was obtained in sprint time between the C protocol (3.300 6 0.105 seconds) and the DYN protocol (3.227 6 0.116 seconds), a further significant improvement of 5.01% was attained between the C and the DYNDJ protocols (3.300 6 0.10 vs. 3.132 6 0.120 seconds; p = 0.001). In addition, a significant improvement (p = 0.001) of 2.93% was observed between the DYN protocol (3.227 6 0.116 seconds) and the DYNDJ protocol (3.132 6 0.116 seconds). The data from this study advocate the use of DYNDJ protocol as a means of significantly improving 20-m sprint performance 1 minute after the DYNDJ protocol.

Coaching Application

Warm-up programs just prior to competition or testing in a 20-yard or 40-yard dash may favorably improve sprint performance when a different, unique exercise, such as depth jumps, are used. Other studies have observed improved sprint times when immediately preceded by a short session of sprint-assisted and sprint-resisted training.

This study also provides a reminder that the warm-up period prior each workout session offers the opportunity to meet multiple training objectives: core temperature elevation, dynamic stretching of key areas involved in the sprinting action, sprint form and technique improvement, and improved sprint performance. The NASE 5-Step Model utilizes a warm-up session with dynamic stretching exercises that also improve sprinting form and technique. This approach saves valuable coaching time, especially during the in-season period, and provides daily devotion to critical areas that often are neglected in team sports.

Reference

Byrne, PJ, Kenny, J, and O’ Rourke, B. Acute potentiating effect of depth jumps on sprint performance. J Strength Cond Res 28 (3): 610–615, 2014