Relationship Between Force-Velocity Characteristics and Sprint Performance in Elite Sprinters: A Pilot Study

BACKGROUND

Sprinting is a type of running that consists of producing a short and intense effort in order to perform maximal speed in a short period of time. Sprinting is widely investigated because of the multiple and complex mechanisms involved. Sprint studies are now focusing on how to improve performance by focusing their analyses on the mechanic variables. The hamstrings are part of the most important muscle groups during sprinting because of their role of stabilization and propulsion, but they must be able to produce the maximum strength during a short moment, this ability is characterized by rate of torque development (RTD). The main of this study was to investigate the association between hamstring RTD (Nm.s-1.kg-1) and mechanical variables composed of maximal power output (Pmax) (W.kg-1), maximal theoretical velocity (V0) (m.s-1), and maximal horizontal force production (F0) (N.kg-1) on short sprints in elite sprinters.

METHODS

For this clinical trial, we used a research method based on data collection. A single group composed of four male and one female elite sprinters (age: 17.2 ± 1.79 years) has been included in this study. The sprinters performed a hamstring strength test, which included five trials of four seconds for each leg. This test required a portable dynamometer, the Kforce®, to collect 100 and 200 milliseconds RTD. Then the subjects were submitted to a sprint test. My Sprint® application has been used to collect the sprint mechanical variables. The sprint test included two trials; a starting block has been used for this test. A linear regression analysis was used between the rates of torque development and mechanical variables composed of maximal power output (Pmax) (W.kg-1), maximal theoretical velocity (V0) (m. s-1), and maximal horizontal force production (F0) (N.kg-1).

RESULTS

No significant correlation was observed between 100 and 200 ms hamstring RTD and sprint biomechanical variables: maximal power output (Pmax) (W.kg-1), maximal theoretical velocity (V0) (m. s-1), and horizontal force production (F0) (N.kg-1). However, 100 and 200 ms RTD collected on the dominant leg tends to be more correlated with maximal theoretical velocity (spearman's rho = 0.80; p-value = 0.13) and Pmax output (spearman's rho = 0.70; p-value = 0.23) while for non-dominant leg, RTD tends to be more correlated with maximal power output (spearman's rho = 0.60; p-value = 0.35) and horizontal force production (spearman's rho = 0.70; p-value = 0.23).

CONCLUSIONS

Hamstring RTD is not correlated with sprint biomechanical variables in elite sprinters. Further investigations must be made to study the observed trends in this study.

Associations Between Physical Characteristics and Golf Clubhead Speed: A Systematic Review with Meta-Analysis

BACKGROUND

Historically, golf does not have a strong tradition of fitness testing and physical training. However, in recent years, both players and practitioners have started to recognise the value of a fitter and healthier body, owing to its potential positive impacts on performance, namely clubhead speed (CHS).

OBJECTIVE

The aim of this meta-analysis was to examine the associations between CHS (as measured using a driver) and a variety of physical characteristics.

METHODS

A systematic literature search with meta-analysis was conducted using Medline, SPORTDiscus, CINAHL and PubMed databases. Inclusion criteria required studies to have (1) determined the association between physical characteristics assessed in at least one physical test and CHS, (2) included golfers of any skill level but they had to be free from injury and (3) been peer-reviewed and published in the English language. Methodological quality was assessed using a modified version of the Downs and Black Quality Index tool and heterogeneity assessed via the Q statistic and I2. To provide summary effects for each of the physical characteristics and their associations with CHS, a random effects model was used where z-transformed r values (i.e. zr) were computed to enable effect size pooling within the meta-analysis.

RESULTS

Of the 3039 studies initially identified, 20 were included in the final analysis. CHS was significantly associated with lower body strength (zr = 0.47 [95% confidence intervals {CI} 0.24-0.69]), upper body strength (zr = 0.48 [95% CI 0.28-0.68]), jump displacement (zr = 0.53 [95% CI 0.28-0.78]), jump impulse (zr = 0.82 [95% CI 0.63-1.02]), jumping peak power (zr = 0.66 [95% CI 0.53-0.79]), upper body explosive strength (zr = 0.67 [95% CI 0.53-0.80]), anthropometry (zr = 0.43 [95% CI 0.29-0.58]) and muscle capacity (zr = 0.17 [95% CI 0.04-0.31]), but not flexibility (zr = - 0.04 [95% CI - 0.33 to 0.26]) or balance (zr =  - 0.06 [95% CI - 0.46 to 0.34]).

CONCLUSIONS

The findings from this meta-analysis highlight a range of physical characteristics are associated with CHS. Whilst significant associations ranged from trivial to large, noteworthy information is that jump impulse produced the strongest association, upper body explosive strength showed noticeably larger associations than upper body strength, and flexibility was not significant. These findings can be used to ensure practitioners prioritise appropriate fitness testing protocols for golfers.

Influence of muscle strength, power, and rapid force capacity on maximal club head speed in male national level golfers

This study investigated the relationships between maximal club head speed (CHS) and physiological and anthropometric parameters in 21 national-level male golfers (age: 21.9 ± 3.9 years; handicap: +1.1 ± 1.7). Maximal isometric strength (MVC) was measured during isometric mid-thigh pull and bench press, while MVC and rate of force development (RFD) were measured during isometric leg press. Power, lower limb stiffness, positive impulse, jump height and RFDdyn were measured during countermovement jump (CMJ). Moreover, rotational trunk power, active range of motion (AROM) and anthropometrics were determined. Comparisons were made between participants with high (FTG) and low (STG) CHS, respectively. FTG demonstrated greater isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power, and CMJ parameters (except RFDdyn) as well as reduced hip AROM compared to STG (P < 0.01). CHS was positively correlated to isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power and CMJ parameters (P < 0.01). In conclusion, strong positive correlations were observed between maximal CHS and maximal strength and power parameters. Consequently, improving maximal neuromuscular strength and power may be considered of importance for golfers, as greater CHS and accompanying driving distance may lead to competitive advantages.

Relationships between highly skilled golfers' clubhead velocity and kinetic variables during a countermovement jump

Previous research has sought to establish the relationship countermovement jump (CMJ) performance has with clubhead velocity (CHV). However, these investigations either assessed lower skilled golfers, or utilised field-based protocols, which are unable to assess a number of biomechanical variables. Fifty highly skilled golfers performed CMJs on Kistler force platforms in laboratory conditions. The CMJ variables included positive impulse, net impulse, average power, peak power, peak force, force at zero velocity and jump height. Clubhead velocity was measured using a TrackMan 3e launch monitor at a driving range. A Pearsons correlation was employed to measure the strength and direction of the relationships between CHV and CMJ derived performance variables. Results indicated strong positive relationships (all p's <0.001) between CHV and positive impulse (r = 0.695), net impulse (r = 0.689), average power (r = 0.645), peak power (r = 0.656), peak force (r = 0.517) and force at zero velocity (r = 0.528) with no significant relationship with jump height. However, if investigators only have access to field-based protocols, it is recommended that they measure jump height and utilise inverse dynamics to calculate take-off velocity. By multiplying take-off velocity by mass, this allows the attainment of net impulse.

Pedal to the Metal: Velocity and Power in High-Level Golfers

ABSTRACT

Parker, J, and Lundgren, LE. Pedal to the metal: Velocity and power in high-level golfers. J Strength Cond Res 35(12): 3425-3431, 2021-In most rotational power assessments, discrete variables are used for subsequent examination; however, movements are continuous, and data can be collected in time series. The purpose of this investigation was to examine the velocity- and power-time series characteristics of a standing rotation test and identify relationships with golf performance. Thirty-one golfers performed a golf-specific rotation test (GSRT) with 3 different resistances (6, 10, and 14 kg) in a robotic engine system. Time series of velocity and power was calculated from the raw data, and each repetition was then normalized to 0-100%. Principal component analyses (PCAs) were performed on velocity and power waveforms. The PCA used an eigenvalue analysis of the data covariance matrix. The relationship between clubhead speed (CHS) and all principal components (PC) was examined using linear regression. Ten velocity parameters and 6 power parameters explained 80% of the variance in the data. For velocity, the first 2 PCs identified both magnitude and phase shift features while PCs 3-5 identified difference features. For power, the first 2 PCs identified both magnitude and phase shift features, the third PC identified a phase shift feature, and the fourth PC identified a difference feature. The highest relationship with CHS was shown for GSRT with 14 kg in PC2 for power (R2 = 0.48, p < 0.001). The PCA of the GSRT power test could distinguish intraindividual differences, external loads, and sex-based differences. Athletes should focus on accelerating smoothly through the movement, particularly with heavier loads, and not pulling aggressively at the beginning of the rotational movement to achieve maximum power.

Drive leg ground reaction forces and rate of force development over consecutive windmill softball pitches

BACKGROUND

Windmill softball pitching is a highly skilled movement, combining whole body coordination with explosive force. Successful pitching requires sequential movement to transfer energy produced by the lower extremity to the pitching arm. Therefore, drive leg ground reaction force (GRF) and the time over which a pitcher can develop force during push off, defined as rate of force development (RFD), is essential for optimal performance. The purpose of this study was to examine GRF and RFD in the drive leg during the windmill softball pitch, as well as pitch velocity, throughout a simulated game.

METHODS

Fourteen softball pitchers (17.9±2.3 years, 166.4±8.7cm, 72.2±12.6kg) pitched a simulated game. Pitch velocity and anterior-posterior and vertical GRF and RFD, each normalized to body weight, were collected for each inning. Average pitch speed remained consistent across all seven innings, 49.57±0.42mph. Changes in GRF and RFD were assessed, with level of significance set as p<0.05.

RESULTS

A one-way repeated measures analysis of variance showed no significant differences in apGRF%BW (p=0.297), vGRF%BW (p=0.574), apRFD (BW/s) (p=0.085) and vRFD (BW/s) (p=0.059).

CONCLUSIONS

Training programs can be improved with the knowledge of the magnitude and rate in which forces are developed by the drive leg during push-off of the windmill softball pitch.

Association of anthropometrics and physical performance measures to golf-specific variables in collegiate male golfers

BACKGROUND

As physical fitness has become more of a central component of competitive golf it is important to have an understanding of the relationship between anthropometric and physical performance on actual golf performance. Thus, the purpose of this investigation was to determine the relationship between measures of anthropometrics and physical performance to golf swing performance.

METHODS

Fourteen division I collegiate golfers performed a battery of tests including the vertical jump, grip strength, rotational medicine ball toss, and sit and reach test in addition to anthropometric measure measurements. Golf specific variables included clubhead speed (CHS), ball velocity (BV) and carry distance (CD) using the participants own driver. Pearson product moment correlations were used to assess the level of relationship between all variables.

RESULTS

Statistically significant large positive relationships were found between grip strength and all golf specific variables. Height also showed large significant positive relationship with both CHS and BV.

CONCLUSIONS

The association between anthropometrics and physical performance and golf specific variables appear to be limited in a group of collegiate male golfers, outside of grip strength. However, this does not mean that physical fitness is irrelevant to golf performance, but caution should be taken in assuming increase in physical performance will have a direct impact on the golf specific variables.

The correlations between physical attributes and golf clubhead speed: A systematic review with quantitative analyses

Clubhead speed (CHS) is a commonly assessed golf performance measure and has been demonstrated to increase in response to physical training. Knowledge of the physical attributes that correlate with CHS will aid in developing effective testing and training protocols for golfers. Thus, the purpose of this review was to identify studies that evaluated the correlation between physical attributes and CHS and synthesise the correlation coefficients using three-level meta-analytic methods. Physical attributes were categorised first by general physical attribute categories. Pooled correlations were also estimated for specific attributes (e.g. jump height, body mass) that were evaluated across three or more studies. The results suggested that CHS had the strongest correlations with measures of upper body power/explosiveness (r = 0.51, 95% confidence interval [95CI]: 0.34, 0.67), lower body strength (r = 0.46; 95CI: 0.27, 0.66), upper body strength (r = 0.41; 95CI: 0.18, 0.63), and lower body power/explosiveness (r = 0.38; 95CI: 0.23, 0.53). Muscle endurance (r = 0.18; 95CI: 0.07, 0.28) and anthropometrics (r = 0.27; 95CI: 0.12, 0.42) had small, but significant correlations, while flexibility (r = 0.03; 95CI: -0.08, 0.14) had a trivial correlation. Several specific assessments such as squat strength, estimated jump power, and medicine ball throw outcomes had large pooled correlations with CHS (r = 0.55-0.63). Overall, the results suggest that measures of muscle strength and power/explosiveness have moderate-large correlations with CHS. Flexibility measures did not have significant associations with CHS, but this may be a result of the specific measures used within the literature.

The Relationship between Isometric Force-Time Characteristics and Dynamic Performance: A Systematic Review

The purpose of this article was to review the data on the relationship between multi-joint isometric strength test (IsoTest) force-time characteristics (peak force, rate of force development and impulse) and dynamic performance that is available in the current literature. Four electronic databases were searched using search terms related to IsoTest. Studies were considered eligible if they were original research studies that investigated the relationships between multi-joint IsoTest and performance of dynamic movements; published in peer-reviewed journals; had participants who were athletes or active individuals who participate in recreational sports or resistance training, with no restriction on sex; and had full text available. A total of 47 studies were selected. These studies showed significant small to large correlations between isometric bench press (IBP) force-time variables and upper body dynamic performances (r² = 0.221 to 0.608, p < 0.05) and significant small to very large correlation between isometric squat (ISqT) (r² = 0.085 to 0.746, p < 0.05) and isometric mid-thigh pull (IMTP) (r² = 0.120 to 0.941, p < 0.05) force-time variables with lower body dynamic performances. IsoTest force-time characteristics were shown to have small to very large correlations with dynamic performances of the upper and lower limbs as well as performance of sporting movements (r² = 0.118 to 0.700, p < 0.05). These data suggest that IsoTest force-time characteristics provide insights into the force production capability of athletes which give insight into dynamic performance capabilities.

Isometric Midthigh Pull Performance Is Associated With Athletic Performance and Sprinting Kinetics in Division I Men and Women's Basketball Players

Townsend, JR, Bender, D, Vantrease, WC, Hudy, J, Huet, K, Williamson, C, Bechke, E, Serafini, PR, and Mangine, GT. Isometric midthigh pull performance is associated with athletic performance and sprinting kinetics in Division I men and women's basketball players. J Strength Cond Res 33(10): 2665-2673, 2019- The relationships between isometric mid-thigh pull (IMTP) force, athletic performance measures, and sprint kinetics in Division I men's and women's basketball players were investigated. Twenty-three (male = 8, female = 15) Division 1 basketball players completed a maximal 20-m sprint trial while tethered to a device that provided kinetic feedback (peak and average sprinting power, velocity and force). Additionally, 1 repetition maximum (1RM) front squat, 1RM hang clean, vertical jump height, and agility (proagility and lane agility) tests were performed. Rate of force development (RFD) at 50, 100, 150, 200 and 250 milliseconds of IMTP and peak force (PF) were also collected. Pearson's product-moment correlation analysis was used to examine the relationships between these measures. Significant (p ≤ 0.05) relationships were observed between IMTP PF and sprint time over all distances (5-20 m; r = -0.62 to 0.69), average sprint velocity (r = 0.50-0.70), peak sprint velocity (r = 0.50-0.54), average sprint force (r = 0.48-0.69), and average sprint power (r = 0.62-0.73). Sprinting kinetic measures (average force and power) over the first 5 m were also significantly (p ≤ 0.05) related to IMTP RFD (50-250 ms; r = 0.42-0.62). Results indicate that IMTP variables are significantly associated with 20-m sprint kinetics. Specifically, IMTP RFD appears to be related to the initial acceleration kinetics of a sprint. Strength and conditioning professionals can possibly implement the IMTP for improved assessment and monitoring of athletic performance and training.

Physical Determinants of Golf Swing Performance: A Review

Sheehan, WB, Bower, RG, and Watsford, ML. Physical determinants of golf swing performance: A review. J Strength Cond Res XX(X): 000-000, 2019-Traditionally, golf practice has primarily focused on the mental, technical, and skill aspects as the primary means to improve performance. Only recently has a greater emphasis been placed on the physical components with balance, muscular strength, power, and specific muscle-tendon properties demonstrating positive associations with club head speed and carry distance. Accordingly, this review will explore the influence of these physical components on measures of golf swing performance. Superior balance may allow players to effectively deal with the need to shift weight during the swing as well as different stance positions, whereas superior lower-body muscular strength, power, and stiffness may allow more mechanical work to be performed on the club during the swing per unit of time, consequently increasing club head speed. Alternatively, flexibility may also contribute to enhanced force production with a greater range of motion, particularly when generating the "X-factor," allowing for a longer backswing and more time to produce higher angular velocities and forces. Furthermore, training intervention studies focusing on the aforementioned components have demonstrated enhancements in swing performance. Targeting multiple muscle groups, including those implicated via electromyography activation, and utilizing multiple modalities have proven effective at increasing club head speed. However, such multifaceted programs have made it difficult to determine the mechanisms that specifically contribute to performance gains. Despite these limitations, strength, power, and musculotendinous stiffness, particularly in the lower body, seem to be stronger determinants of club head speed and carry distance than flexibility. Furthermore, acute improvements can be induced using resistance-orientated warm-ups.

Relationships Between Highly Skilled Golfers' Clubhead Velocity and Vertical Ground Reaction Force Asymmetry During Vertical Jumps and an Isometric Midthigh Pull

Wells, JET, Mitchell, ACS, Charalambous, LH, and Fletcher, IM. Relationships between highly skilled golfers' clubhead velocity and vertical ground reaction force asymmetry during vertical jumps and an isometric midthigh pull. J Strength Cond Res 34(10): 2824-2831, 2020-Clubhead velocity (CHV) is a commonly measured variable within golf due to strong associations with increased drive distance. Previous research has revealed significant relationships between CHV and vertical ground reaction force (vGRF) variables during bilateral tasks including a countermovement jump (CMJ), squat jump (SJ), drop jump (DJ), and isometric midthigh pull (IMTP). Asymmetries have been linked to performance outcomes in a number of sports; however, few studies have assessed asymmetries within golf. The current study, therefore, examined the relationships between CHV and vGRF asymmetries for CMJ positive impulse, SJ positive impulse, DJ positive impulse, and IMTP peak force (PF). Furthermore, the level of agreement for asymmetries between protocols was assessed by using Kappa coefficients. Fifty highly skilled (handicap ≤5) male golfers attended laboratory and range-based testing sessions. Positive impulse and PF were measured using a dual force platform system, with CHV measured using a TrackMan 3e launch monitor. There was no significant relationship (r = -0.14 to 0.22) between CHV and each of the vGRF asymmetry measures. Of the golfers tested, 26 had a "real" asymmetry in the CMJ, 18 had a "real" asymmetry in the SJ, 25 had a "real" asymmetry in the DJ, and 27 had a "real" asymmetry in the IMTP. Kappa coefficients indicated that asymmetries rarely favored the same limb (k = 0.06 to 0.39) with asymmetries varying for individual golfers between protocols. As such, asymmetries are neither beneficial nor detrimental to CHV but are inherently individual and dependent on the task.

Effect of Sampling Frequency on Isometric Midthigh-Pull Kinetics

PURPOSE

Skeletal-muscle function can be evaluated using force-times curves generated via the isometric midthigh pull (IMTP). Various sampling frequencies (500-1000 Hz) have been used for IMTP assessments; however, no research has investigated the influence of sampling frequency on IMTP kinetics. Therefore, the purpose of this study was to investigate the influence of sampling frequency on kinetic variables during the IMTP, including peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) at 3 time bands (0-100, 0-150, 0-200 ms).

METHODS

Academy rugby league players (n = 30, age 17.5 ± 1.1 y, height 1.80 ± 0.06 m, mass 85.4 ± 10.3 kg) performed 3 IMTP trials on a force platform sampling at 2000 Hz, which was subsequently down-sampled to 1500, 1000, and 500 Hz for analysis.

RESULTS

Intraclass correlation coefficients (ICC) and coefficients of variation (CV) demonstrated high within-session reliability for all force and RFD variables across all sampling frequencies (ICC ≥ .80, CV ≤ 14.4%) except RFD 0-100 and 0-150, which demonstrated slightly greater levels of variance (CV = 18.0-24.1%). Repeated-measures analysis of variance revealed no significant differences (P > .05, Cohen d ≤ 0.0171) in kinetic variables between sampling frequencies. Overall, high reliability was observed across all sampling frequencies for peak force, time-specific force, and RFD 0- to 200-ms variables, with no significant differences (P > .05) for each kinetic variable across sampling frequencies.

CONCLUSIONS

Practitioners and scientists may consider sampling as low as 500 Hz when measuring peak force, time-specific force values, and RFD at predetermined time bands during the IMTP for accurate and reliable data.

Multi-joint rate of force development testing protocol affects reliability and the smallest detectible difference

Isometric tests have been used to assess rate of force development (RFD), however variation in testing methodologies are known to affect performance outcomes. The aim of this study was to assess the RFD in the isometric squat (ISqT) using two test protocols and two testing angles. Eleven participants (age: 26.8 ± 4.5 years, strength training experience: 7.1 ± 3.03 years) completed test and retest sessions one week apart, whereby two test protocols with respect to duration and instructions were compared. Isometric peak force (ISqT^peak) and isometric explosive force (ISqT^exp) tests were assessed at two joint angles (knee flexion angle 100° and 125°). Force-time traces were sampled and subsequently analysed for RFD measures. Average and instantaneous RFD variables did not meet reliability minimum criteria in ISqT^peak at 100° or 125°. The ISqT^exp test at 100° met reliability criteria in the RFD 0-200 and 0-250ms variables. The ISqT^exp test at 125° met reliability criteria in the RFD 0-150, 0-200 and 0-250ms variables. Force-time characteristics were optimized at the higher knee joint angle. Average and instantaneous RFD measures obtained using a traditional peak force test do not meet basic reliability criteria. Researchers assessing multi-joint RFD should employ the explosive RFD test protocol as opposed to the traditional isometric peak force protocol.

Between-Session Reliability of Isometric Midthigh Pull Kinetics and Maximal Power Clean Performance in Male Youth Soccer Players

Dos'Santos, T, Thomas, C, Comfort, P, McMahon, JJ, Jones, PA, Oakley, NP, and Young, AL. Between-session reliability of isometric midthigh pull kinetics and maximal power clean performance in male youth soccer players. J Strength Cond Res 32(12): 3373-3381, 2018-The aim of the study was to determine the between-session reliability of isometric midthigh pull (IMTP) kinetics and maximal weight lifted during the power clean (PC) in male youth soccer players, and to identify the smallest detectable differences between sessions. Thirteen male youth soccer players (age: 16.7 ± 0.5 years, height: 1.80 ± 0.08 m, and mass: 70.5 ± 9.4 kg) performed 3 IMTP trials, whereas only 10 soccer players performed maximal PCs. These were performed twice, separated by 48 hours to examine the between-session reliability. Intraclass correlation coefficients (ICCs) and coefficient of variation (CV) demonstrated high levels of within-session (ICC = 0.84-0.98, CV = 4.05-10.00%) and between-session reliability (ICC = 0.86-0.96, CV = 3.76-7.87%) for IMTP kinetics (peak force [PF] and time-specific force values 30-250 ms) and maximal PC (ICC = 0.96, CV = 3.23%), all meeting minimum acceptable reliability criteria. No significant differences (p > 0.05, effect size ≤0.22) were revealed between sessions for IMTP kinetics and maximal PC performance. Strength and conditioning coaches and practitioners should consider changes of >6.04% in maximal PC and changes in IMTP kinetics of >14.31% in force at 30 ms, >14.73% in force at 50 ms, >12.36% in force at 90 ms, >12.37% in force at 100 ms, >14.51% in force at 150 ms, >11.71% in force at 200 ms, >7.23% in force at 250 ms, and >8.50% in absolute PF as meaningful improvements in male youth soccer players. Decrements in the IMTP kinetics greater than the aforementioned values could possibly be used as an indicator of neuromuscular fatigue and preparedness for training or competition.

Surfing the Waves of the CMJ; Are There between-Sport Differences in the Waveform Data?

The ability to analyse countermovement jump (CMJ) waveform data using statistical methods, like principal component analysis, can provide additional information regarding the different phases of the CMJ, compared to jump height or peak power alone. The aim of this study was to investigate the between-sport force-time curve differences in the CMJ. Eighteen high level golfers (male = 10, female = 8) and eighteen high level surfers (male = 10, female = 8) performed three separate countermovement jumps on a force platform. Time series of data from the force platform was normalized to body weight and each repetition was then normalized to 0–100 percent. Principal component analyses (PCA) were performed on force waveforms and the first six PCs explained 35% of the variance in force parameters. The main features of the movement cycles were characterized by magnitude (PC1 and PC5), waveform (PC2 and PC4), and phase shift features (PC3). Surf athletes differ in their CMJ technique and show a greater negative centre of mass displacement when compared to golfers (PC1), although these differences are not necessarily associated with greater jump height. Principal component 5 demonstrated the largest correlation with jump height (R² = 0.52). Further studies are recommended in this area, to reveal which features of the CMJ that relate to jumping performance, and sport specific adaptations.

A Comparison of the Isometric Midthigh Pull and Isometric Squat: Intraday Reliability, Usefulness, and the Magnitude of Difference Between Tests

PURPOSE

To examine the reliability and usefulness of the isometric midthigh pull (IMTP) and isometric squat (ISqT) performed at the same knee and hip angles. The scores produced in each test were compared to determine the magnitude of differences between tests.

METHODS

Twenty-six male and female athletes (age, 23.6 [4.3] y; height, 1.75 [0.07] m; and body mass, 68.8 [9.7] kg) performed 2 maximal repetitions of the IMTP and ISqT following a specific warm-up.

RESULTS

Maximum force, absolute peak force (PF), relative PF, allometrically scaled PF, rate of force development (0-200 and 0-250 ms), and impulse (0-300 ms) were deemed reliable (intraclass correlation coefficient [ICC] ≥.86 and coefficient of variation [CV] ≤9.4%) in the IMTP and ISqT based on predetermined criteria (ICC ≥.8 and CV ≤10%). Impulse (0-200 and 0-250 ms) was reliable in the ISqT (ICC ≥.92 and CV ≤9.9%). Participants produced significantly (P < .05) greater PF and impulse (0-300 ms) during the ISqT compared with the IMTP. When split by sex, female participants produced significantly greater PF (P = .042) during the ISqT, with no significant differences among male participants (P = .245). Both tests are capable of detecting changes in performance in maximum force and absolute PF.

CONCLUSIONS

Both tests are reliable for non-time-dependent maximal strength measures when measured at the same knee and hip angles. The ISqT may be preferred when coaches want to test an athlete's true maximum lower-limb strength, especially female athletes.

Effect of Different Onset Thresholds on Isometric Midthigh Pull Force-Time Variables

Dos'Santos, T, Jones, PA, Comfort, P, and Thomas, C. Effect of different onset thresholds on isometric midthigh pull force-time variables. J Strength Cond Res 31(12): 3463-3473, 2017-Various thresholds have been used to identify the onset of contraction during isometric midthigh pull (IMTP); however, no agreed onset threshold exists for this assessment. The purpose of this study was to compare relative body weight (BW) and arbitrary onset thresholds to a criterion onset threshold 5 SDs of BW for IMTP force-time variables; force at each threshold, peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) during 0-100, 0-150, 0-200 ms. Academy rugby league players (n = 9, age: 18.5 ± 0.4 years; height: 1.82 ± 0.09 m; mass: 91.2 ± 13.1 kg) performed 2 IMTP trials on a force platform sampling at 1,000 Hz. The neutral force-time data pool (18 trials) was analyzed with five different thresholds and compared with criterion threshold to determine any variance in force-time variables. Five SDs of BW were significantly lower than 10% BW and 75 N for threshold force which led to significantly greater time-specific force values at 100 and 150 ms and unacceptable limits of agreements (LOA) for all force-time variables. No significant differences (p > 0.05) were observed between 2.5% and 5 SDs of BW; and between 5% and 5 SDs of BW for threshold force and all force-time variables with acceptable LOA. The 5 SDs of BW and 2.5% BW onset thresholds consistently resulted in the lowest values for threshold force, time-specific force values, and RFD, attributed to a lower onset bias. Therefore, scientists and practitioners are recommended to use a 5 SD of BW onset threshold for time-specific force values and RFD for accurate data because it accounts for signal noise during the weighing period. Subsequently, there is greater certainty that the onset of contraction identifies a true meaningful change in force, in contrast to relative BW thresholds.

A review of the reliability of biomechanical variables produced during the isometric mid-thigh pull and isometric squat and the reporting of normative data

The use of isometric strength testing, particularly the isometric mid-thigh pull (IMTP) has increased dramatically over the last decade. The IMTP and isometric squat (ISqT) provide one aspect of performance monitoring with variables such as peak force and rate of force development being derived from the force-time curve. The reliability of some of these variables is conflicting in the literature, and the reporting of the reliability is not standardised across the research. The majority of research only reports intraclass correlation coefficients with very few studies reporting coefficient of variation and 90% confidence intervals. Additionally, methods used to calculate variables from the force-time curve differ across studies. An aim of muscle strength testing is to provide normative values for specific sports, allowing coaches to distinguish between performance levels or evaluate the effects of training on performance. This narrative review aims to evaluate studies that have researched the reliability and/or reported normative data for both tests. Additionally, the testing protocols and the force-time curve analysis techniques utilised are discussed, concluding with practical applications for coaches on the uses and limitations of these tests. Results demonstrate that peak force is the most reliable measure and can be used to determine maximum strength capabilities.

Relationships between highly skilled golfers' clubhead velocity and force producing capabilities during vertical jumps and an isometric mid-thigh pull

Whilst previous research has highlighted significant relationships between golfers' clubhead velocity (CHV) and their vertical jump height and maximum strength, these field-based protocols were unable to measure the actual vertical ground reaction force (vGRF) variables that may correlate to performance. The aim of this study was to investigate relationships between isometric mid-thigh pull (IMTP), countermovement jump (CMJ), squat jump (SJ) and drop jump (DJ) vGRF variables and CHV in highly skilled golfers. Twenty-seven male category 1 golfers performed IMTP, CMJ, SJ and DJ on a dual force platform. The vertical jumps were used to measure positive impulse during different stretch-shortening cycle velocities, with the IMTP assessing peak force (PF) and rate of force development (RFD). Clubhead velocity was measured using a TrackMan launch monitor at a golf driving range. Pearsons correlation coefficient analyses revealed significant relationships between peak CHV and CMJ positive impulse (r = 0.788, p < 0.001), SJ positive impulse (r = 0.692; p < 0.001), DJ positive impulse (r = 0.561, p < 0.01), PF (r = 0.482, p < 0.01), RFD from 0-150 ms (r = 0.343, p < 0.05) and RFD from 0-200 ms (r = 0.398, p < 0.05). The findings from this investigation indicate strong relationships between vertical ground reaction force variables and clubhead velocity.

Physical Characteristics of Youth Elite Golfers and Their Relationship With Driver Clubhead Speed

Coughlan, D, Taylor, M, Jackson, J, Ward, N, and Beardsley, C. Physical characteristics of youth elite golfers and their relationship with driver clubhead speed. J Strength Cond Res 34(1): 212-217, 2020-Increased clubhead speed (CHS) has a strong relationship with golf performance and is related to athletic qualities in adult golfers. Research investigating the youth golfer is limited. The purpose of this study was to explore the relationships between strength and power on CHS in youth golfers. A correlational design was used to assess relationships between CHS and anthropometric, strength, and power measurements. Thirty-six male and 33 female golfers aged 13-17 took part in this study. Male golfers showed significant relationships between CHS and handicap (HCP) (r = -0.50), seated medicine ball throw to the left (SMBTL) (r = 0.67), and right (SMBTR) (r = 0.61), rotational medicine ball throw to the left (RMBTL) (r = 0.71), and right RMBTR (r = 0.62). Female golfers showed significant relationships between CHS and HCP (r = -0.52), mass (r = 0.72), countermovement jump power (r = 0.60), RMBTL (r = 0.57), RMBTR (r = 0.56). Multiple stepwise linear regression analysis identified 77% of the variance in CHS could be explained through SMBTL and RMBTL in males. In females, 84% of the variance in CHS could be explained through mass, RMBTR, and height. This study demonstrated relationships between CHS and body mass and upper-, lower-, and full-body concentric dominant power exercises. This study could aid in the development of training interventions for youth golfers.

Relationships between Isometric Force-Time Characteristics and Dynamic Performance

The purpose of this study was to explore the relationships between isometric mid-thigh pull (IMTP) force-time characteristics (peak force and time-specific force vales (100⁻250 ms)) and dynamic performance and compare dynamic performance between stronger and weaker athletes. Forty-three athletes from different sports (rowing, soccer, bicycle motocross, and hockey) performed three trials of the squat jump (SJ), countermovement jump (CMJ), and IMTP, and performed a one repetition maximum power clean (PC). Reactive strength index modified (RSImod) was also calculated from the CMJ. Statistically significant large correlations between IMTP force-time characteristics and PC (ρ = 0.569⁻0.674, p < 0.001), and moderate correlations between IMTP force-time characteristics (excluding force at 100 ms) and RSImod (ρ = 0.389⁻0.449, p = 0.013⁻0.050) were observed. Only force at 250 ms demonstrated a statistically significant moderate correlation with CMJ height (ρ = 0.346, p = 0.016) and no statistically significant associations were observed between IMTP force-time characteristics and SJ height. Stronger athletes (top 10) demonstrated statistically significantly greater CMJ heights, RSImods, and PCs (p ≤ 0.004, g = 1.32⁻1.89) compared to weaker (bottom 10) athletes, but no differences in SJ height were observed (p = 0.871, g = 0.06). These findings highlight that the ability to apply rapidly high levels of force in short time intervals is integral for PC, CMJ height, and reactive strength.

Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-Aged Males

We sought to determine the effects of L-leucine (LEU) or different protein supplements standardized to LEU (~3.0 g/serving) on changes in body composition, strength, and histological attributes in skeletal muscle and adipose tissue. Seventy-five untrained, college-aged males (mean ± standard error of the mean (SE); age = 21 ± 1 years, body mass = 79.2 ± 0.3 kg) were randomly assigned to an isocaloric, lipid-, and organoleptically-matched maltodextrin placebo (PLA, n = 15), LEU (n = 14), whey protein concentrate (WPC, n = 17), whey protein hydrolysate (WPH, n = 14), or soy protein concentrate (SPC, n = 15) group. Participants performed whole-body resistance training three days per week for 12 weeks while consuming supplements twice daily. Skeletal muscle and subcutaneous (SQ) fat biopsies were obtained at baseline (T1) and ~72 h following the last day of training (T39). Tissue samples were analyzed for changes in type I and II fiber cross sectional area (CSA), non-fiber specific satellite cell count, and SQ adipocyte CSA. On average, all supplement groups including PLA exhibited similar training volumes and experienced statistically similar increases in total body skeletal muscle mass determined by dual X-ray absorptiometry (+2.2 kg; time p = 0.024) and type I and II fiber CSA increases (+394 μm² and +927 μm²; time p < 0.001 and 0.024, respectively). Notably, all groups reported increasing Calorie intakes ~600–800 kcal/day from T1 to T39 (time p < 0.001), and all groups consumed at least 1.1 g/kg/day of protein at T1 and 1.3 g/kg/day at T39. There was a training, but no supplementation, effect regarding the reduction in SQ adipocyte CSA (−210 μm²; time p = 0.001). Interestingly, satellite cell counts within the WPC (p < 0.05) and WPH (p < 0.05) groups were greater at T39 relative to T1. In summary, LEU or protein supplementation (standardized to LEU content) does not provide added benefit in increasing whole-body skeletal muscle mass or strength above PLA following 3 months of training in previously untrained college-aged males that increase Calorie intakes with resistance training and consume above the recommended daily intake of protein throughout training. However, whey protein supplementation increases skeletal muscle satellite cell number in this population, and this phenomena may promote more favorable training adaptations over more prolonged periods.

The Validity and Responsiveness of Isometric Lower Body Multi-Joint Tests of Muscular Strength: a Systematic Review

Background

Researchers and practitioners working in sports medicine and science require valid tests to determine the effectiveness of interventions and enhance understanding of mechanisms underpinning adaptation. Such decision making is influenced by the supportive evidence describing the validity of tests within current research. The objective of this study is to review the validity of lower body isometric multi-joint tests ability to assess muscular strength and determine the current level of supporting evidence.

Methods

Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were followed in a systematic fashion to search, assess and synthesize existing literature on this topic. Electronic databases such as Web of Science, CINAHL and PubMed were searched up to 18 March 2015. Potential inclusions were screened against eligibility criteria relating to types of test, measurement instrument, properties of validity assessed and population group and were required to be published in English. The Consensus-based Standards for the Selection of health Measurement Instruments (COSMIN) checklist was used to assess methodological quality and measurement property rating of included studies. Studies rated as fair or better in methodological quality were included in the best evidence synthesis.

Results

Fifty-nine studies met the eligibility criteria for quality appraisal. The ten studies that rated fair or better in methodological quality were included in the best evidence synthesis. The most frequently investigated lower body isometric multi-joint tests for validity were the isometric mid-thigh pull and isometric squat. The validity of each of these tests was strong in terms of reliability and construct validity. The evidence for responsiveness of tests was found to be moderate for the isometric squat test and unknown for the isometric mid-thigh pull. No tests using the isometric leg press met the criteria for inclusion in the best evidence synthesis.

Conclusions

Researchers and practitioners can use the isometric squat and isometric mid-thigh pull with confidence in terms of reliability and construct validity. Further work to investigate other validity components such as criterion validity, smallest detectable change and responsiveness to resistance exercise interventions may be beneficial to the current level of evidence.

Electronic supplementary material

The online version of this article (doi:10.1186/s40798-017-0091-2) contains supplementary material, which is available to authorized users.

Electromyographic Analysis of the Lower Limb Muscles in Low- and High-Handicap Golfers

PURPOSE

The aim of this study was to compare the electromyographic patterns of the lower limb muscles during a golf swing performed by low- and high-handicap golfers.

METHOD

Ten golfers (5 low- and 5 high-handicap) performed 8 swings using a 7-iron. Surface electromyography (EMG) was recorded for the following lower limb muscles on both sides: biceps femoris, semitendinosus, gluteus maximus, vastus medialis and lateralis, rectus femoris, tibialis anterior, peroneus longus, and gastrocnemius medialis and lateralis. The golf-swing phases were determined by 3-dimensional high-speed video analysis.

RESULTS

Compared with the high-handicap golfers, the low-handicap golfers performed the forward swing with a shorter duration of the swing phases, with the exception of the late follow-through, where they exhibited longer duration. Considering the EMG patterns, the low-handicap golfers showed a tendency for the studied muscles to reach an activation peak earlier and presented statistically significant higher muscle activity in some of the lower limb muscles, mainly from the left side.

CONCLUSION

Differences between low- and high-handicap golfers were found in the average duration of swing phases and in the activation level of the lower limbs, with more evidence on muscles from the left side.

A comparison of methods for determining the rate of force development during isometric midthigh clean pulls

Twelve female division I collegiate volleyball players were recruited to examine the reliability of several methods for calculating the rate of force development (RFD) during the isometric midthigh clean pull. All subjects were familiarized with the isometric midthigh clean pull and participated in regular strength training. Two isometric midthigh clean pulls were performed with 2 minutes rest between each trail. All measures were performed in a custom isometric testing device that included a step-wise adjustable bar and a force plate for measuring ground reaction forces. The RFD during predetermined time zone bands (0-30, 0-50, 0-90, 0-100, 0-150, 0-200, and 0-250 milliseconds) was then calculated by dividing the force at the end of the band by the band's time interval. The peak RFD was then calculated with the use of 2, 5, 10, 20, 30, and 50 milliseconds sampling windows. The average RFD (avgRFD) was calculated by dividing the peak force (PF) by the time to achieve PF. All data were analyzed with the use of intraclass correlation alpha (ICCα) and the coefficient of variation (CV) and 90% confidence intervals. All predetermined RFD time bands were deemed reliable based on an ICCα >0.95 and a CV <4%. Conversely, the avgRFD failed to meet the reliability standards set for this study. Overall, the method used to assess the RFD during an isometric midthigh clean pull impacts the reliability of the measure and predetermined RFD time bands should be used to quantify the RFD.

Effect of knee and trunk angle on kinetic variables during the isometric midthigh pull: test-retest reliability

The isometric midthigh pull (IMTP) has been used to monitor changes in force, maximum rate of force development (mRFD), and impulse, with performance in this task being associated with performance in athletic tasks. Numerous postures have been adopted in the literature, which may affect the kinetic variables during the task; therefore, the aim of this investigation was to determine whether different knee-joint angles (120°, 130°, 140°, and 150°) and hip-joint angles (125° and 145°), including the subjects preferred posture, affect force, mRFD, and impulse during the IMTP. Intraclass correlation coefficients demonstrated high within-session reliability (r ≥ .870, P < .001) for all kinetic variables determined in all postures, excluding impulse measures during the 130° knee-flexion, 125° hip-flexion posture, which showed a low to moderate reliability (r = .666-.739, P < .001), while between-sessions testing demonstrated high reliability (r > .819, P < .001) for all kinetic variables. There were no significant differences in peak force (P > .05, Cohen d = 0.037, power = .408), mRFD (P > .05, Cohen d = 0.037, power = .409), or impulse at 100 ms (P > .05, Cohen d = 0.056, power = .609), 200 ms (P > .05, Cohen d = 0.057, power = .624), or 300 ms (P > .05, Cohen d = 0.061, power = .656) across postures. Smallest detectable differences demonstrated that changes in performance of >1.3% in peak isometric force, >10.3% in mRFD, >5.3% in impulse at 100 ms, >4.4% in impulse at 200 ms, and >7.1% in impulse at 300 ms should be considered meaningful, irrespective of posture.