Strength improvements in skeletal muscle that has not been directly activated during training has been reported for a number of years (2,21,23). Several studies have reported enhanced strength performances in the untrained limb during unilateral strength training (2,4). This phenomenon is usually defined as “cross-education,” and has been suggested to be related with both neural and hormonal factors (4,7). It has been suggested that the neural adaptations associated with “cross-education” involve increased motor output from spinal motoneurons, and some form of motor learning related to neural plasticity of the motor cortex, premotor complex, and cerebellum (5).
A transfer effect has also been observed between the lower and upper body (13,27), Madarame et al. (27) reported increased arm muscle size and strength when lower-body resistance exercises with blood flow restriction were added to the upper-body training program. Others have reported a greater relative effect in upper-body isometric strength gains when lower-body training was combined with upper-body training compared with upper-body training only (13). The investigators also reported an augmented hormonal response to a whole-body training program, compared with exercising with the upper body only. To the best of our knowledge, only 2 investigations have examined the effects of lower-body resistance training on upper-body strength performance, and both reported greater increases in arm strength when legs were trained simultaneously (13,27). However, whether the transfer effect on upper-body strength improvement is greater using a high-intensity (HI) strength training protocol or a high-volume strength training protocol for the lower body is not well understood.
The longer duration of time under tension during high-volume training sessions (10–15 repetitions per set at 60–70% of 1 repetition maximum (1RM)), may result in reduced muscle oxygenation, which may play a critical role in growth hormone stimulation (9,15,19,24,25). Considering that growth hormone is an anabolic hormone with relevant effects in the regulation of metabolism (31), it is likely that high-volume training sessions performed with the lower body may have a greater impact on body composition than lower body HI training sessions. Thus, the purpose of this study was to compare the effect of a lower body hypertrophy training program (5 sets of 10–12 reps at 65–70% of 1RM with 2 minutes and 15 seconds recovery time between each set) to a maximal strength lower-body training program (5 sets of 4–5 reps at 88–90% of 1RM with 3 minutes recovery time between each set) on upper body strength and power adaptation.
Experimental Approach to the Problem
Participants were randomly assigned to 2 experimental groups and provided a 6-week training program. The first group (HI group) performed a HI training program for both upper and lower body. The second group (mixed high volume and high-intensity program (MP) group) followed a training program focused on muscle hypertrophy for lower body and a HI protocol for the upper body. Participants were assessed before and after the training period for body composition, maximal strength, and power of both upper and lower body. Participants were also requested to not participate in any other training or competition.
Twenty experienced resistance-trained men volunteered to participate in this study. To be considered for the study, participants were required to be between the age of 18 and 35 years, and have a minimum of 3 years of free weights resistance training experience (mean ± SD; 4.25 ± 1.6 years). Exclusion criteria included the use of performance enhancing drugs and injuries occurred at least 1 year before the investigation. Participants were familiar with all the exercises used in this study, and they typically trained with a load permitting between 8–10 reps in the previous 4 months before this present investigation. Participants were randomly assigned to one of the 2 groups; group 1 (HI; mean ± SD; n = 9; age = 24.9 ± 2.9 years; body mass = 88.7 ± 17.2 kg; height = 177.0 ± 5.6 cm) used a HI program for both upper and lower-body exercises, group 2 (MP; n = 11; age = 26.0 ± 4.7 years; body mass = 82.8 ± 9.1 kg; height = 177.5 ± 5.9 cm) used a HI protocol for the upper-body exercises and a high-volume program for the lower-body exercises. All participants signed an informed consent document and the study was approved by the “Alma Mater Studiorum—University of Bologna” bioethics committee. Participants were asked to maintain their normal diet throughout the study.
Both training programs were composed of the same exercises that are shown in Table 1. All participants exercised 4 days per week for 6 weeks. The HI and MP group used the identical HI training program for the upper body. Both groups performed 5 sets of 5 reps at 88% in the first 4 weeks, and 5 sets of 4 reps at 90% in the last 2 weeks of training for the upper-body exercises. Recovery time between each set was of 2 minutes and 15 seconds. The HI groups used the same HI protocol for the lower-body exercises, whereas the MP group followed a training program that focused on muscle hypertrophy. Participants in MP performed 5 sets of 12 reps at 65% of their 1RM for the first 4 weeks, and 5 sets of 10 reps at 70% of their 1RM during the last 2 weeks of training. Recovery time between each set was 1 minute. The upper-body training program always preceded the lower-body training program. Subjects were encouraged to increase the resistance used per workout if they performed the maximum number of repetitions required for 2 consecutive exercise sessions. If the participants were not able to obtain the number of repetitions provided, then the load was reduced in the subsequent set to enable completion of the required number of repetitions for each training protocol. No forced or assisted reps were used in either protocol. All training sessions were supervised by certified coaches. Participants recorded all workouts in a logbook, which was collected by one of the investigators after each workout. Feedback was provided regarding changes in load used per exercise.
Anthropometric and Performance Assessments
Body mass was determined to the nearest 0.1 kg using a standard mechanical weighing scale (Detecto, Missouri, USA). Skinfold measurements (collected by a Lange Skinfold Caliper; Cambridge Scientific Industries, Cambridge, USA) and anthropometric measures were used to examine changes in body composition. Body density was estimated with a 7-site skinfold test (22) and the body fat percentage was calculated using Siri equation (32). Estimation of middle arm muscle area (AMA) was performed using the formula of Heimsfield (16):
Middle arm circumference and skinfold were measured midway between the acromion and olecranon process of the left arm. Intraclass coefficients were 0.96 (SEM: 3.13 cm2; MD: 2.2 cm2) and 0.99 (SEM: 0.74 kg; MD: 0.92 kg) for AMA and fat mass (FM), respectively. The same investigators performed all the anthropometric analyses during each assessment period.
Participants did not train for 2 days before the strength assessments to allow for appropriate recovery. Before the testing protocol, each participant performed a standardized warm-up based on previously published literature (28). The warm-up consisted of 5 minutes of cycling at a cadence of 70 rpm and intensity of 70 W, 10 body weight squats, 10 walking lunges, 10 walking “knee hugs,” and 10 walking “butt kicks” (28).
Upper-body power was assessed through the seated medicine ball throw (29). Participants were asked to throw rubber medicine balls weighing 2, 3 and 4 kg. All throws required the participants to sit on the floor against a wall and push the medicine ball from the center of the chest with both hands. Participants were required to remain in contact with the wall during the test. Each participant had 3 attempts to throw as far as possible. Rest time between each attempt was 45 seconds. The distance of each throw was measured using a 20-m fiberglass tape. The longest throw was recorded. Intraclass coefficients (ICC) were 0.82 (SEM: 0.32 m; MD: 0.74 m), 0.86 (SEM: 0.23 m; MD: 0.63 m), and 0.90 (SEM: 0.18 m; MD: 0.48 m) for the 2-, 3- and 4-kg medicine ball throw, respectively.
During each testing session, participants performed a maximal effort isometric mid-thigh pull on a force plate (500 Hz; Kisler Force Plate, Winterthur, Switzerland). Bar height was adjusted to obtain a knee angle of 120°. Grip width was also measured to reproduce the same position in all testing sessions. Once grip position was established, participants were strapped to the bar and were instructed to pull as hard as possible, and with maximum explosive intent (11). Each participant performed 2 trials with a 3-minute recovery time between each trial. Force-time curves were recorded and analyzed to calculate peak force (PF) and the peak rate of force development (pRFD). As suggested by Haff et al. (12), the pRFD was calculated as the highest RFD during 20 millisecond sampling windows (pRFD 20). ICC's were 0.92 (SEM: 164.29 N; MD: 346.6 N) and 0.87 (SEM: 1,349.58 N·s−1; MD: 3,248.7 N·s−1) for the PF and pRFD 20, respectively.
Maximal dynamic strength of the upper body was assessed by a 1RM bench press. Bench press testing was performed in the standard supine position. The participant lowered the bar to mid chest and then pressed the weight until his arms were fully extended. Participants were required to pause briefly at the end of the lowering phase and wait for a signal before starting the concentric phase. Lower body maximal dynamic strength was also assessed by a 1RM free barbell parallel squat. Participants were asked to reach a position where the greater trochanter of the femur was at the same level of the knee. A 3-minute recovery time between each attempt was observed. The bench press and squat 1RM test were conducted as previously described by Hoffman (18). ICC's were 0.98 (SEM: 3.06 kg; MD: 5.48 kg) and 0.95 (SEM: 7.20 kg; MD: 18.9 kg) for the 1RM bench press and squat 1RM, respectively.
After maximal strength assessments, a power test for the bench press exercise was achieved using 30% (POW30) and 50% (POW50) of the previously established 1RM bench press. Participants were required to perform a single repetition for each load with maximal velocity. Participants performed 2 attempts for each load, with a 3-minute recovery time. The highest value obtained between the 2 single repetitions was registered. An optical encoder (Globus Real Power; Globus Inc., Treviso, Italia) connected to a personal computer was used for power assessment. ICC's were 0.94 (SEM: 18.59 W; MD: 51.5 W) and 0.88 (SEM: 26.97 W; MD: 44.7 W) for the POW30 and POW50, respectively.
A Shapiro-Wilk test was used to test the normal distribution of the data. Data were statistically analyzed using separate 1-way analysis of covariance for anthropometric and performance measures. The pretest and the posttest values were used as covariate and dependent variable, respectively. For effect size (ES), the partial eta squared statistic was reported and according to Green and colleagues (10) 0.01, 0.06, and 0.14 represented small, medium, and large ES, respectively. The significance level was set at p ≤ 0.05. Where appropriate, percent change was calculated as follows: (posttest mean—pretest mean)/(pretest mean) × 100. All data are reported as mean ± SD. Data were analyzed using SPSS v22 software (SPSS, Inc., Chicago, IL, USA).
Anthropometric parameters of both HI and MP are reported in Table 2. The analysis of covariance (ANCOVA) indicated a significant difference (F1,18 = 48.81; p = 0.009; η2 = 3.41) after adjusting for pretest differences between the groups for FM. A decrease in FM was noted in MP group (−0.9 ± 1.02 kg), whereas HI group showed a slightly increased on this parameter (0.02 ± 0.78 kg). Significant differences between the groups at posttest were noted for AMA (F1,17 = 4.62; p = 0.046; η2 = 0.214) after adjusting for pretest differences. The MP group showed an average increase of 5.8% after the training, whereas the increase was of 1.7% in HI group. No significant group differences were observed for fat free mass (F1,17 = 3.26; p = 0.088; η2 = 0.161) and body mass (F1,17 = 0.02; p = 0.967; η2 < 0.001).
Strength and power performances measures of HI and MP are reported in Tables 3 and 4, respectively. The ANCOVA indicated a significant difference (F1,18 = 9.31; p = 0.007; η2 = 0.354) among the group means for posttest 1RM bench press values after adjusting for pretest differences. After the training intervention, the 1RM bench press showed an increase of 7.2% and of 2.1% in MP and in HI group, respectively. A significant difference (F1,18 = 8.11; p = 0.011; η2 = 0.323) was also observed for POW50 values, after adjusting for pretest differences. Power expression was significantly different in MP group (+8.6%) compared with HI (−0.78%). No significant differences between the 2 groups at posttest were noted for maximal isometric strength expressed at the mid-thigh pull (F1,18 = 4.10, p = 0.059, η2 = 0.194), pRFD 20 (F1,18 = 0.52; p = 0.479; η2 = 0.030), 1RM squat (F1,18 = 1.35; p = 0.264; η2 = 0.082), and for POW30 (F1,18 = 4.30; p = 0.053; η2 = 0.202). No significant differences between the groups were also observed for the 2-kg (F1,18 = 0.01; p = 0.916; η2 = 0.001), 3-kg (F1,18 = 0.13; p = 0.724; η2 = 0.007), and 4-kg (F1,18 = 0.70; p = 0.415; η2 = 0.039) medicine ball throws.
The results of this study indicate that a 6-week strength training program using a combination of high volume and HI resistance training for lower-body exercises and upper-body exercises, respectively, promoted a greater increase in upper-body strength, power, and arm muscle size compared with a HI only training program. Although significant increases were observed in anthropometric measures (fat free mass and AMA), and in maximal and dynamic strength for both MP and HI, participants in MP experienced a significantly greater increase in 1RM bench press and in POW50 compared with HI.
The resistance training protocols used were focused on maximal strength and hypertrophy development, and not on muscle power development. Interestingly, a significant increase in bench press power occurred in MP only. Although several studies have reported that strength gains are velocity specific (6), increases in maximal strength may cause a positive shift of the force-power curve (3,30). Considering that participants in MP experienced a significantly greater increase in upper-body maximal strength and muscle hypertrophy compared with HI, this may provide some explanation for these results. The greater gains in arms muscle size occurred in the MP group suggest that anabolic effects of high-volume sessions of squat may stimulate gains on upper-body muscles. The high-intensity squat workouts, comprising 5 sets of 3–4 reps, may not have been sufficient to activate a transfer effect between the lower and the upper body. Training sessions characterized by high training volumes are associated with greater changes in circulating levels of anabolic hormones compared with higher intensity workouts focused on maximal strength (8,15). As reported by Linnamo et al. (26), hormonal changes seem to be related to the amount muscle mass activated, and to the training protocol used. Although speculative, the high-volume training protocol, involving large muscle mass exercises in the lower body, likely, stimulated an increase in circulating plasma GH concentrations. The elevation in this anabolic hormone circulating throughout the body may have also influenced protein synthesis in the upper body musculature as well.
A transfer effect between the lower and upper body may be also related to neural mechanisms. Cross-education has been extensively studied in relation to injured limb and immobilization (17). Reduction in strength during limb immobilization, when the healthy limb was trained, has been attributed to complex mechanisms such as motor irradiation (4) and hemispheric interaction (20) that emanate from the spinal cord and cortical brain areas. Although some investigators have reported that neural factors have only little to no transfer effect from the lower to upper body (13), others have suggested that intensive lower-body training could influence arm strength by reducing inhibitory feedback from the Ib afferent nerves from Golgi tendon organs (1). Inhibitory interneurons activated by Golgi organs can be downregulated by corticospinal pathways stimulated by strength training (1). Both central and peripheral neural mechanisms, enhanced by high-volume training sessions for lower body, may have stimulated neural adaptations in motor units not directly involved in lower-body exercises. Although both MP and HI training group included lower-body strength training, the high-volume training sessions in MP were characterized by a longer time under tension compared with the high-intensity workouts of HI program (10–12 reps compared with 4–5 reps). The squat exercise has been recognized as a “whole-body” exercise, not involving just the lower-body muscles but also torso extensors and shoulder muscles (33). The prolonged upper body and arm muscle isometric contractions performed to sustain the barbell during the high-volume sessions may have further stimulated upper body muscle strength and size adaptations. To the best of our knowledge, no experimental studies have investigated arms and shoulder muscle activation in the back squat at different exercise intensities. Prolonged upper-body muscle activation during the squat exercise may be an important mechanical factor for stimulating muscle adaptation in the upper body. The potential for strength improvement in experienced, strength-trained individuals are significantly lower compared with untrained subjects (14). This study suggests that high volume, lower-body strength training can provide a greater stimulus for increasing upper-body strength and power in a resistance-trained population. Although a significant difference between the 2 groups was found for the loss of FM during the training period, the variation was beyond the measurement error for this parameter.
The results of this study confirm the hypothesis that lower-body training can affect upper-body adaptations to a HI training program in experienced, resistance-trained men. Results of this study provide evidence to support the use of different training schemes for upper and lower body during the same training period for optimizing upper body adaptations in men. In particular, greater improvements in upper-body maximal strength and power can be achieved using high-volume training programs to optimize upper body adaptations to resistance training. It also may provide support for the use of a multifocal approach to program design, similar to what may be used in nonlinear training programs.
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