Paul Comfort

Relationships Between Strength, Sprint, and Jump Performance in Well-Trained Youth Soccer Players

Abstract Comfort, P, Stewart, A, Bloom, L, and Clarkson, B. Relationships between strength, sprint, and jump performance in well-trained youth soccer players. J Strength Cond Res 28(1): 173–177, 2014—Research has demonstrated a clear relationship between absolute and relative strength and sprint and jump performance in adult athletes; however, this relationship in younger athletes has been less extensively studied. The aim of this study, therefore, was to determine the relationships between strength, sprint, and jump performances in well-trained youth soccer players. Thirty-four young male soccer players (17.2 ± 0.6 years; body mass, 72.62 ± 7.42 kg; height, 179.27 ± 6.58 cm) performed a predicted maximal squat test, 20-m sprints, squat jumps (SJs), and countermovement jumps (CMJs). Absolute strength showed the strongest correlations with 5-m sprint times (r = −0.596, p < 0.001, power = 0.99), SJ height (r = 0.762, p < 0.001, power = 1.00), and CMJ height (r = 0.760, p < 0.001, power = 1.00), whereas relative strength demonstrated the strongest correlation with 20-m sprint times (r = −0.672, p < 0.001, power = 0.99). The results of this study illustrate the importance of developing high levels of lower-body strength to enhance sprint and jump performance in youth soccer players, with stronger athletes demonstrating superior sprint and jump performances.

COMPARISONS OF PEAK GROUND REACTION FORCE AND RATE OF FORCE DEVELOPMENT DURING VARIATIONS OF THE POWER CLEAN

Comfort, P, Allen, M, and Graham-Smith, P. Comparisons of peak ground reaction force and rate of force development during variations of the power clean. J Strength Cond Res 25(5): 1235-1239, 2011-The aim of this investigation was to determine the differences in vertical ground reaction forces and rate of force development (RFD) during variations of the power clean. Elite rugby league players (n = 11; age 21 ± 1.63 years; height 181.56 ± 2.61 cm; body mass 93.65 ± 6.84 kg) performed 1 set of 3 repetitions of the power clean, hang-power clean, midthigh power clean, or midthigh clean pull, using 60% of 1-repetition maximum power clean, in a randomized order, while standing on a force platform. Differences in peak vertical ground reaction forces (Fz) and instantaneous RFD between lifts were analyzed via 1-way analysis of variance and Bonferroni post hoc analysis. Statistical analysis revealed a significantly (p < 0.001) greater peak Fz during the midthigh power clean (2,801.7 ± 195.4 N) and the midthigh clean pull (2,880.2 ± 236.2 N) compared to both the power clean (2,306.24 ± 240.47 N) and the hang-power clean (2,442.9 ± 293.2 N). The midthigh power clean (14,655.8 ± 4,535.1 N·s−1) and the midthigh clean pull (15,320.6 ± 3,533.3 N·s−1) also demonstrated significantly (p < 0.001) greater instantaneous RFD when compared to both the power clean (8,839.7 ± 2,940.4 N·s−1) and the hang-power clean (9,768.9 ± 4,012.4 N·s−1). From the findings of this study, when training to maximize peak Fz and RFD the midthigh power clean and midthigh clean pull appear to be the most advantageous variations of the power clean to perform.

Kinetic comparisons during variations of the power clean

Comfort, P, Allen, M, and Graham-Smith, P. Kinetic comparisons during variations of the power clean. J Strength Cond Res 25(12): 3269–3273, 2011—The aim of this investigation was to determine the differences in peak power, peak vertical ground reaction forces, and rate of force development (RFD) during variations of the power clean. Elite rugby league players (n = 16; age 22 ± 1.58 years; height 182.25 ± 2.81 cm; body mass 98.65 ± 7.52 kg) performed 1 set of 3 repetitions of the power clean, hang power clean, midthigh power clean, or midthigh clean pull, using 60% of 1 repetition maximum power clean, in a randomized order, while standing on a force platform. One-way analysis of variance with Bonferroni post hoc analysis revealed a significantly (p < 0.001) greater peak power output during the midthigh power clean (3,565.7 ± 410.6 W) and the midthigh clean pull (3,686.8 ± 386.5 W) compared with both the power clean (2,591.2 ± 645.5 W) and the hang power clean (3,183.6 ± 309.1 W), along with a significantly (p < 0.001) greater peak Fz during the midthigh power clean (2,813.8 ± 200.5 N) and the midthigh clean pull (2,901.3 ± 226.1 N) compared with both the power clean (2,264.1 ± 199.6 N) and the hang power clean (2,479.3 ± 267.6 N). The midthigh power clean (15,049.8 ± 4,415.7 N·s−1) and the midthigh clean pull (15,623.6 ± 3,114.4 N·s−1) also demonstrated significantly (p < 0.001) greater instantaneous RFD when compared with both the power clean (8,657.9 ± 2,746.6 N·s−1) and the hang power clean (10,314.4 ± 4,238.2 N·s−1). From the findings of this study, when training to maximize power, Fz, and RFD, the midthigh power clean and midthigh clean pull appear to be the most advantageous variations of the power clean to perform.

Determination of optimal loading during the power clean, in collegiate athletes.

Abstract Comfort, P, Fletcher, C, and McMahon, JJ. Determination of optimal loading during the power clean, in collegiate athletes. J Strength Cond Res 26(11): 2970–2974, 2012—Although previous research has been performed in similar areas of study, the optimal load for the development of peak power during training remains controversial, and this has yet to be established in collegiate level athletes. The purpose of this study was to determine the optimal load to achieve peak power output during the power clean in collegiate athletes. Nineteen male collegiate athletes (age 21.5 ± 1.4 years; height 173.86 ± 7.98 cm; body mass 78.85 ± 8.67 kg) performed 3 repetitions of power cleans, while standing on a force platform, using loads of 30, 40, 50, 60, 70, and 80% of their predetermined 1-repetition maximum (1RM) power clean, in a randomized, counterbalanced order. Peak power output occurred at 70% 1RM (2,951.7 ± 931.71 W), which was significantly greater than the 30% (2,149.5 ± 406.98 W, p = 0.007), 40% (2,201.0 ± 438.82 W, p = 0.04), and 50% (2,231.1 ± 501.09 W, p = 0.05) conditions, although not significantly different when compared with the 60 and 80% 1RM loads. In addition, force increased with an increase in load, with peak force occurring at 80% 1RM (1,939.1 ± 320.97 N), which was significantly greater (p < 0.001) than the 30, 40, 50, and 60% 1RM loads but not significantly greater (p > 0.05) than the 70% 1RM load (1,921.2 ± 345.16 N). In contrast, there was no significant difference (p > 0.05) in rate of force development across loads. When training to maximize force and power, it may be advantageous to use loads equivalent to 60–80% of the 1RM, in collegiate level athletes.

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.

A comparison of maximal squat strength and 5-, 10-, and 20-meter sprint times, in athletes and recreationally trained men.

Abstract Comfort, P, Bullock, N, and Pearson, SJ. A comparison of maximal squat strength and 5-, 10-, and 20-meter sprint times, in athletes and recreationally trained men. J Strength Cond Res 26(4): 937–940, 2012—The purpose of this study was to identify whether there was a relationship between relative strength during a 1 repetition maximum (1RM) back squat and 5-, 10-, and 20-m sprint performances in both trained athletes and recreationally trained individuals. Professional rugby league players (n = 24) and recreationally trained individuals (n = 20) participated in this investigation. Twenty-meter sprint time and 1RM back squat strength, using free weights, were assessed on different days. There were no significant (p ≥ 0.05) differences between the well-trained and recreationally trained groups for 5-m sprint times. In contrast, the well-trained groups 10- and 20-m sprint times were significantly quicker (p = 0.004; p = 0.002) (1.78 + 0.06 seconds; 3.03 + 0.09 seconds) compared with the recreationally trained group (1.84 + 0.07 seconds; 3.13 + 0.11 seconds). The athletes were significantly stronger (170.63 + 21.43 kg) than the recreationally trained individuals (135.45 + 30.07 kg) (p = 0.01); however, there were no significant differences (p > 0.05) in relative strength between groups (1.78 + 0.27 kg/kg; 1.78 + 0.33 kg/kg, respectively). Significant negative correlations were found between 5-m sprint time and relative squat strength (r = −0.613, power = 0.96, p = 0.004) and between relative squat strength and 10- and 20-m sprint times in the recreationally trained group (r = −0.621, power = 0.51, p = 0.003; r = −0.604, power = 0.53, p = 0.005, respectively). These results, indicating that relative strength, are important for initial sprint acceleration in all athletes but more strongly related to sprint performance over greater distances in recreationally trained individuals.

The Effect of Loading on Kinematic and Kinetic Variables During the Midthigh Clean Pull

Abstract Comfort, P, Udall, R, and Jones, PA. The effect of loading on kinematic and kinetic variables during the midthigh clean pull. J Strength Cond Res 26(5): 1208–1214, 2012—The ability to develop high levels of muscular power is considered a fundamental component for many different sporting activities; however, the load that elicits peak power still remains controversial. The primary aim of this study was to determine at which load peak power output occurs during the midthigh clean pull. Sixteen participants (age 21.5 ± 2.4 years; height 173.86 ± 7.98 cm; body mass 70.85 ± 11.67 kg) performed midthigh clean pulls at intensities of 40, 60, 80, 100, 120, and 140% of 1 repetition maximum (1RM) power clean in a randomized and balanced order using a force plate and linear position transducer to assess velocity, displacement, peak power, peak force (Fz), impulse, and rate of force development (RFD). Significantly greater Fz occurred at a load of 140% (2,778.65 ± 151.58 N, p < 0.001), impulse within 100, 200, and 300 milliseconds at a load of 140% 1RM (196.85 ± 76.56, 415.75 ± 157.56, and 647.86 ± 252.43 N·s, p < 0.023, respectively), RFD at a load of 120% (26,224.23 ± 2,461.61 N·s−1, p = 0.004), whereas peak velocity (1.693 ± 0.042 m·s−1, p < 0.001) and peak power (3,712.82 ± 254.38 W, p < 0.001) occurred at 40% 1RM. Greatest total impulse (1,129.86 ± 534.86 N·s) was achieved at 140% 1RM, which was significantly greater (p < 0.03) than at all loads except the 120% 1RM condition. Results indicate that increased loading results in significant (p < 0.001) decreases in peak power and peak velocity during the midthigh clean pull. Moreover, if maximizing force production is the goal, then training at a higher load may be advantageous, with peak Fz occurring at 140% 1RM.

AN ELECTROMYOGRAPHICAL COMPARISON OF TRUNK MUSCLE ACTIVITY DURING ISOMETRIC TRUNK AND DYNAMIC STRENGTHENING EXERCISES

Comfort, P, Pearson, SJ, and Mather, D. An electromyographical comparison of trunk muscle activity during isometric trunk and dynamic strengthening exercises. J Strength Cond Res 25(X): 000-000, 2010-The purpose of this study was to compare rectus abdominis and erector spinae muscle activity during isometric (prone bridge [PB] and superman [SM]) and dynamic strengthening exercises (back squat, front squat [FS], and military press). Participants (n = 10, age 21.8 ± 2.6 years; body mass 82.65 ± 10.80 kg, 174.5± 7.2 cm), performed each exercise in a randomized order, using a repeated-measures design. Electromyographical (EMG) activity (sampling at 2,000 Hz) of the rectus abdominis (RA) and the erector spinae (ES) muscles was recorded throughout the duration of the exercises. Intraclass correlations demonstrated the highest levels of reliability for muscle activity during the isometric exercises; however, all exercises demonstrated high level of reliability (r = 0.764-0.998, p ≤ 0.01). The PB demonstrated significantly greater (p < 0.01) RA activity compared to all other exercises. The ES activity was significantly (p < 0.01) greater during the FS (1.010 ± 0.308 root mean square value [RMS (V)]) and SM (0.951 ± 0.217 RMS[V]) and compared to all other exercises, although there was no significant difference (p > 0.05) between the FS and the SM exercise. The PB may be the most suitable exercise for strengthening the RA, compared to dynamic exercises at a low to moderate load, because of a higher level of muscle activity. The FS may be a useful alternative to isometric exercises when strengthening the ES, because it results in slightly higher muscle activity levels when using only a light to moderate load. Because of the dynamic nature of the FS, this may also be more beneficial in transferring to activities of daily living and sporting environments.

Complex training in ice hockey: the effects of a heavy resisted sprint on subsequent ice-hockey sprint performance.

Matthews, MJ, Comfort, P, and Crebin, R. Complex training in ice hockey: the effects of a heavy resisted sprint on subsequent ice-hockey sprint performance. J Strength Cond Res 24(11): 2883-2887, 2010-The aim of the study was to investigate the acute effect of a heavy resisted sprint when used as a preload exercise to enhance subsequent 25-m on-ice sprint performance. Eleven competitive ice-hockey players (mean ± SD: Age = 22.09 ± 3.05 years; Body Mass = 83.47 ± 11.7 kg; Height = 1.794 ± 0.060 m) from the English National League participated in a same-subject repeated-measures design, involving 2 experimental conditions. During condition 1, participants performed a 10-second heavy resisted sprint on ice. Condition 2 was a control, where participants rested. An electronically timed 25-m sprint on ice was performed before and 4 minutes after each condition. The results indicated no significant difference (p = 0.176) between pre (3.940 + 0.258 seconds) and post (3.954 + 0.261 seconds) sprint times in the control condition. The intervention condition, however, demonstrated a significant 2.6% decrease in times (p = 0.02) between pre (3.950 + 0.251 seconds) and post (3.859 + 0.288 seconds) test sprints. There was also a significant change (p = 0.002) when compared to the times of the control condition. These findings appear to suggest that the intensity and duration of a single resisted sprint in this study are sufficient to induce an acute (after 4 minutes of rest) improvement in 25-m sprint performance on ice. For those athletes wishing to improve skating speed, heavy resisted sprints on ice may provide a biomechanically suitable exercise for inducing potentiation before speed training drills.

An Investigation Into the Relationship Between Maximum Isometric Strength and Vertical Jump Performance.

Abstract Thomas, C, Jones, PA, Rothwell, J, Chiang, CY, and Comfort, P. An investigation into the relationship between maximum isometric strength and vertical jump performance. J Strength Cond Res 29(8): 2176–2185, 2015—Research has demonstrated a clear relationship between dynamic strength and vertical jump (VJ) performance; however, the relationship of isometric strength and VJ performance has been studied less extensively. The aim of this study was to determine the relationship between isometric strength and performance during the squat jump (SJ) and countermovement jump (CMJ). Twenty-two male collegiate athletes (mean ± SD; age = 21.3 ± 2.9 years; height = 175.63 ± 8.23 cm; body mass = 78.06 ± 10.77 kg) performed isometric midthigh pulls (IMTPs) to assess isometric peak force (IPF), maximum rate of force development, and impulse (IMP) (I100, I200, and I300). Force-time data, collected during the VJs, were used to calculate peak velocity, peak force (PF), peak power (PP), and jump height. Absolute IMTP measures of IMP showed the strongest correlations with VJ PF (r = 0.43–0.64; p ⩽ 0.05) and VJ PP (r = 0.38–0.60; p ⩽ 0.05). No statistical difference was observed in CMJ height (0.33 ± 0.05 m vs. 0.36 ± 0.05 m; p = 0.19; ES = –0.29) and SJ height performance (0.29 ± 0.06 m vs. 0.33 ± 0.05 m; p = 0.14; ES = –0.34) when comparing stronger to weaker athletes. The results of this study illustrate that absolute IPF and IMP are related to VJ PF and PP but not VJ height. Because stronger athletes did not jump higher than weaker athletes, dynamic strength tests may be more practical methods of assessing the relationships between relative strength levels and dynamic performance in collegiate athletes.