Effects of Eccentric Contraction Duration on Muscle Strength, Power Production, Vertical Jump and Soreness
Prior research has investigated the effects of either eccentric-only training or comparing eccentric and concentric exercise on changes related to strength and power expression, but no research to date has investigated the impact of altering the duration of either the concentric or eccentric component on these parameters. Therefore, the purpose of this study was to assess the duration of eccentric (i.e. 2-second, 4-second vs. 6-second) muscle contractions and their effect on muscle strength, power production, vertical jump and soreness using a plate-loaded barbell Smith squat exercise. Thirty college-aged males (23 ± 3.5 years, 178 ± 6.8 cm, 82 ± 12 kg and 11.6 ± 5.1 % fat) with 3.0 ± 1.0 years of resistance training experience and training frequency of 4.3 ± 0.9 days per week were randomized and assigned to one of three eccentric training groups that incorporated different patterns of contraction. For every repetition, all three groups utilized two-second concentric contractions and paused for one second between the concentric and eccentric phases. The control group (2S) utilized two-second-eccentric contractions while the 4S group performed four-second eccentric contractions and the 6S performed six-second eccentric contractions. All repetitions were completed using the barbell Smith squat exercise. All participants completed a four-week training protocol that required them to complete two workouts per week using their prescribed contraction routine for 4 sets of 6 repetitions at an intensity of 80 — 85% 1RM. Two-way mixed factorial ANOVA were used to determine changes among groups. A p-value of 0.05 was used for all statistical determinations. At baseline, no between-group differences (p > 0.05) were found for any anthropometric, 1RM or dietary data with the exception of absolute protein intake (p = 0.03). For all performance data, significant group x time interaction effects were found for average power production across all three sets of a squat jump protocol (p = 0.04) while vertical jump did not reach significance but there was a trend towards a difference (GxT, p = 0.07). No other significant (p > 0.05) group x time interaction effects were found for the performance variables. All groups showed significant main effects for time in 1RM (p < 0.001), vertical jump (p = 0.004), peak power (p < 0.001) and average power (p < 0.001). Peak velocity data indicated that the 6S group experienced a significant reduction in peak velocity during the squat jump protocol as a result of the 4-week training program (p = 0.03). Soreness data revealed significant increases across time in all groups at both week 0 and week 4. Paired sample t-tests revealed greater differences in soreness values across time in the 2S group. The results provide further evidence that resistance training with eccentrically dominated movement patterns can be an effective method to acutely increase maximal strength and power expression in trained college age men. Furthermore, longer eccentric contractions may negatively impact explosive movements such as the vertical jump while shorter eccentric contractions may instigate greater amounts of soreness. These are important considerations for the strength and conditioning professional to more fully understand that expressions of strength and power through eccentric training and varying durations of eccentric activity can have a significant impact for populations ranging from athletes desiring peak performance.
Eccentrics, Health and Physical Education
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