This study examined the amount and time-course of shifts in the moment-knee angle relation of the quadriceps (QF) and hamstring (HAM) muscles in response to different length-restricted strength training regimens. Thirty-two athletes were divided into three different training groups (G1-3): G1 performed isometric training at knee joint angles corresponding to long muscle-tendon unit (MTU) length for QF and HAM; G2 conducted concentric-eccentric contraction cycles that were restricted to a knee joint range of motion corresponding to predominantly long MTU length for QF and HAM; G3 combined the protocols of G1 and G2. Moment-knee angle and EMG-knee angle relations of QF and HAM were measured on five different occasions: two times before, after five and eight weeks of training and four weeks post training. Moments and EMG-data of each subject were normalized to the largest value produced at any knee joint position [% Max.]. Obtained by curve fitting, the optimal knee joint angle for QF moment production was significantly (P<0.05) shifted to longer MTU length in G1 and G3 after 5 weeks of training and in G2 after 8 weeks of training. Contrary, no significant shifts were detected for HAM. Our data suggest that the predominant MTU length during loading is a major trigger for human force-length adaptations.

The purpose of this work was to investigate whether different modes of long-term competitive physical activity cause functional differences in the moment-knee angle relation of the M. quadriceps femoris (QF). Therefore, a sample (n = 40) of young male competitive endurance runners, cyclists, triathletes and tennis players performed isometric maximal voluntary knee extensions (MVC) with their stronger leg at six different knee joint angles while keeping the hip joint angle constant. Muscle activation of QF-muscles during MVC was estimated using surface electromyography (EMG). Moments and EMG data of each subject were normalized to the largest value produced at any knee joint position [% Max.]. No significant differences in the normalized [% Max.] moment-knee angle relation of the QF were found between endurance runners, cyclists and triathletes. Despite few unsystematic exceptions, no functional differences in the normalized moment-knee angle relation of the QF occurred among tennis players and the endurance-oriented athletic groups. Obtained by curve fitting, the optimal knee joint angle for moment production was not significantly different among all athletic groups. We conclude that long-term competitive endurance running, cycling, triathlon and tennis do not provoke functional differences in the moment-knee angle relation of the whole QF.

This study compared traditional (TP) and daily undulating (DUP) periodization on muscle strength, EMG-estimated neural drive and muscle architecture of the quadriceps femoris (QF). 10 non-athletic females (24.4±3.2 years) performed 14 weeks of isometric training for the QF exercising 1 leg using TP and the contralateral leg using DUP. Intensities varied from 60% to 80% of MVC and the intensity zones and training volume were equated for each leg. Knee extension MVC, maximal voluntary QF-EMG activity and vastus lateralis (VL) muscle architecture were measured in both legs before, after 6 weeks and after 14 weeks of training using dynamometry, surface EMG and ultrasonography. Isometric MVC and maximal QF-EMG remained unaltered after 6 weeks of training, but were significantly (P<0.05) enhanced after 14 weeks in both legs (MVC: TP 24%, DUP 23%; QF-EMG: TP 45%, DUP 46%). VL-architecture remained unchanged following 6 weeks of training, but VL-muscle thickness (TP 17%, DUP 16%) and fascicle length (TP 16%, DUP 17%) displayed significant (P<0.05) enlargements after 14 weeks in both legs. Importantly, these temporal neuromuscular alterations displayed no significant differences between the training legs. Therefore, periodization may not act as a key trigger for neuromuscular adaptations.

Ullrich, B, Pelzer, T, Oliveira, S, and Pfeiffer, M. Neuromuscular responses to short-term resistance training with traditional and daily undulating periodization in adolescent elite judoka. J Strength Cond Res 30(8): 2083-2099, 2016-The influence of different periodization models on neuromuscular outcomes after short-term strength training periods has not been examined in adolescent athletes. Eleven elite judoka (age: 14.8 ± 0.6 years, height: 163.2 ± 7.5 cm, body mass: 57.3 ± 11.1 kg, 5 boys/6 girls, and strength training experience: 2.7 ± 1.1 years) performed two 4-week strength training mesocycles (each with 12 sessions) with either traditional (TP) or daily undulating (DUP) periodization. Both mesocycles were separated by a 7-week washout period and added to the regular judo training. Strength training was performed as lifting and lowering of weights using squats, knee flexion curl, clean & jerk, snatch, bench press, barbell bench pull, and lat pull-down. The mesocycles were equated for the number of repetitions and different intensity zones (50-90% of 1 repetition maximum [1RM]), addressing the optimization of strength, power, or velocity. Laboratory and 1RM testing was carried out 2 times during the baseline (T1 and T2), after the TP mesocycle (T3), after the washout period (T4), and after the DUP mesocycle (T5). Isometric knee extensor and knee flexor maximum voluntary contractive capacity (MVC), electromyographic-estimated neural drive of the quadriceps femoris, vastus lateralis (VL) muscle architecture, and 1RMs of all training exercises were measured. ANOVA revealed moderate (5.5-13.5%) but significant (p ≤ 0.05) temporal gains in knee extensor MVC, 1RMs, and VL architecture during both the mesocycles. Wilcoxon tests detected no significant differences for the percentage changes of any outcome between the mesocycles. For adolescent judoka, TP and DUP were equally adept in improving neuromuscular outcomes during short-term training periods.

This study examined squat jumping (SJ) mechanics following length restricted strength training regimens of the knee extensors and flexors. SJ from a 110 degrees knee joint angle starting position and isometric moment-knee angle relations of knee extensors and flexors were analysed in 16 athletes before and directly after 8 weeks of strength training regimens that were restricted to knee joint angles corresponding to long muscle-tendon unit (MTU) length for the knee extensors and flexors. SJ mechanics were studied using a two-dimensional kinematic model with three rigid bodies (upper leg, lower leg, foot) in combination with force plates measurements of ground reaction force in the right and left lower extremity. Centre of mass jumping height significantly (p<0.05) increased post training, but this was not explained by enhanced absolute power generation in the knee joint. However, post training small but significant (p<0.05) shifts to smaller knee joint angles occurred in the normalized [% Max.] knee joint angle dependent power generation in the right and left knee joint during SJ. The isometric moment-knee angle relation of the knee extensors was also significantly (p<0.05) shifted to longer MTU lengths of knee extensors. Length restricted strength training may alter the mechanical situation during both isometric contractions and dynamic athletic movements.

Ullrich, B, Pelzer, T, and Pfeiffer, M. Neuromuscular effects to 6 weeks of loaded countermovement jumping with traditional and daily undulating periodization. J Strength Cond Res 32(3): 660-674, 2018-Loaded vertical jumps are routinely used to enhance athlete's power production in the lower extremity and to optimize jumping and sprinting performance. This study compared traditional (TP) and daily undulating (DUP) periodization on muscle strength, jumping performance, electromyographic (EMG) muscle activity, and muscle architecture during preseason loaded jump training. Twenty-two athletes from different team sports (age: 24.3 ± 2.6 years, height: 175.9 ± 7.5 cm, body mass: 72.2 ± 8.4 kg, 12 males/10 females, strength training experience: 5.1 ± 2.2 years) performed 6 weeks of loaded countermovement jumping (CMJ) (18 sessions) during which subjects arranged the experimental training loads with either TP or DUP. Therefore, loading conditions corresponding to 0, 15, and 30% of individual body mass were used by manipulating weighted training vests and the intensity zones and training volume were equated between the groups. Pre- to post-training, center of mass (COM) maximal CMJ performance, isometric maximal voluntary contractive capacity of the leg extensors (MVC), EMG maximal voluntary muscle activity of knee extensor muscles, and vastus lateralis and rectus femoris muscle architecture were examined. Repeated measures multivariate analysis of variances (MANOVA with factors: time × training group) revealed moderate (5-16%) but significant (p ≤ 0.006) temporal increases in COM jumping height, leg extensor MVC and muscle architecture in both groups. Importantly, these temporal alterations were similar using either TP or DUP. Therefore, our data indicate that both periodization models can be effectively applied to increase leg extensor strength, vertical jumping performance, and muscle architecture during short-term preseason loaded jump training.

This study investigated whether different length-restricted strength training regimens affect voluntary explosive concentric power-load curves of the quadriceps femoris (QF) and hamstring (HAM) muscles. Thirty-two athletes were divided into 3 different training groups (G1-G3): G1 performed isometric training at knee joint angles corresponding to long muscle-tendon unit (MTU) length for QF and HAM; G2 conducted concentric-eccentric contraction cycles that were restricted to a knee joint range of motion corresponding to predominantly long MTU length for QF and HAM; and G3 combined the protocols of G1 and G2. Knee joint angle-dependent power-load curves during maximal voluntary explosive concentric knee extensions and flexions were measured for loads corresponding to 40, 60, and 80% of individual 1 repetition maximum at 5 different occasions: 2 times before, after 5 and 8 weeks of training, and 4 weeks post training. Power values of each subject were normalized to the largest value produced at any knee joint position (percent maximum). Obtained by curve fitting, the optimal knee joint angle for power production of QF and HAM remained unaltered throughout the course of the study for all testing loads and training groups. Therefore, different strength training regimens with a common restriction to long MTU lengths failed to induce length-dependent alterations in athlete's voluntary concentric power-load curves of knee extensors and flexors. The approach to develop strength training programs that induce systematic shifts in length-dependent power production of QF and HAM is of direct practical relevance for athletic activities such as cycling, ice skating, and skiing. However, restricting the muscle excursion range during loading seems to be an inappropriate trigger to cause length-dependent alterations in athlete's voluntary concentric power-load curves.

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