Effect Of Short-term Resistance Training Research Articles

The Effects of Short-Term Resistance Training and Subsequent Detraining on Neuromuscular Function, Muscle Cross-Sectional Area, and Lean Mass

PurposeTo examine and compare the effects of three days of dynamic constant external resistance (DCER) and isokinetic (ISOK) training and subsequent detraining on thigh muscle cross-sectional area (TMCSA) and thigh lean mass (TLM), ISOK peak torque (PT), DCER strength, isometric force, muscle activation, and percent voluntary activation (%VA).MethodsThirty-one apparently-healthy untrained men (mean ± SD age = 22.2 ± 4.2 years; body mass = 77.9 ± 12.9 kg; height = 173.9 ± 5.4 cm) were randomly assigned to a DCER training group (n = 11), ISOK training group (n = 10) or control (CONT) group (n = 10). Subjects visited the laboratory eight times. The first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for unilateral training of the quadriceps (if assigned to a training group), and the last three visits were the post-training assessments conducted at three days, one week, and two weeks after training ended.ResultsDCER strength increased from pre- to post-training assessment 1 in both limbs for the DCER group only, and remained elevated during post-training assessments 2 and 3 (P < 0.05). In addition, surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment, and post-training assessments 1 and 2 (P < 0.05). No other training-related changes were found.ConclusionThe primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training. This has important implications for injury rehabilitation, where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.

An examination of motor unit firing rates during steady torque of maximal efforts with either an explosive or slower rate of torque development.

What is the central question of this study? The aim was to explore agonist and antagonist motor unit firing rates during maximal efforts performed with either an explosive or a slower rate of torque development. What is the main finding and its importance? The antagonist muscle presented a motor unit firing rate relationship similar to the agonist muscle. Additionally, the motor units of both muscles exhibited higher firing rates during explosive maximal contractions than during maximal contractions performed at a slower rate of torque development. These results could prove useful to future research analysing the effects of age, disease, resistance training and/or fatigue-related alterations to motor unit firing rates. The primary purpose of the present study was to examine motor unit (MU) firing rates in agonist and antagonist muscles during periods of steady, maximal efforts using explosive and slower rates of torque development. A secondary purpose was to analyse the MU firing rate versus action potential amplitude relationships of the agonist and antagonist muscles during maximal efforts. Thirteen subjects (mean±SD; age, 21.2±3.6years; mass 81.1±21.3kg; and stature, 177.1±9.9cm) performed two maximal isometric trapezoid muscle actions of the elbow flexors that included either an explosive or a slower, linearly increasing rate (ramp) of torque development. Surface EMG signals of the biceps brachii (BB) and triceps brachii (TB) muscles were collected and decomposed into their constituent MU action potential trains. The MU firing rate versus action potential amplitude relationships of the BB (agonist) and TB (antagonist) muscles were analysed. Moderate to strong relationships (|r|≥0.65) were present for the explosive and ramp contractions in the agonist and antagonist muscles. Firing rates of smaller and larger MUs were higher during the explosive [mean±SD; agonist=18.1±6.9pulses per second (pps), antagonist=22.0±3.9pps] than the ramp (agonist=14.0±5.1pps, antagonist=18.3±4.4pps) contractions for the agonist (P=0.013) and antagonist muscles (P=0.007). The antagonist muscle exhibits a similar MU firing rate versus action potential amplitude relationship to the agonist muscle at maximal efforts. Future research should investigate the effects of short-term resistance training on antagonist firing rates and the involvement of peripheral feedback on firing rates during maximal efforts performed at various rates of torque development.

The effect of short-term resistance training on hand reaction time improvement is independent of sexual dimorphism

Objectiveː The aim was to evaluate the effects of four weeks of resistance training and sexual dimorphism on Manual reaction time in apparently healthy subjects.&#x0D; Methods: The subjects of the sample were randomly allocated in two groups, as follow: Control (CTRL) - kept 4 weeks without any systematized physical activity (Nmales= 8, age= 24±3 yrs., body weight= 76.9±15.4 kg; Nfemales= 8, age= 22.5±4 yrs., body weight= 70.8±17.5 kg); Experimental (EXP) - 4 weeks of resistance training (Nmales= 8, age= 23±3 yrs., weight= 69.6±11 kg; Nfemales= 8, age= 22.5±1 yrs., body weight= 59.77±6.8 kg). The resistance training consisted of 4 exercises for upper limbs (3 sets x 8-12 reps) and 4 exercises for lower (3 sets x 12-15 reps). Manual reaction time was evaluated in a manufactured Arduino-based reaction time device connected to a computer.&#x0D; Results: For men, there was a significant decrease in Manual reaction time after resistance training within EXP (p&lt;0.0001) and between groups (p&lt;0.0001). Women showed the same results within EXP (p&lt;0.0001) and between groups (p&lt;0.0001). Additionally, there was no sexual dimorphism before or after four weeks of resistance training.&#x0D; Conclusion: The results suggest that just four weeks of resistance training was sufficient to improve Manual reaction time, regardless of sexual dimorphism. Therefore, resistance training inclusion in the training periodization seems essential to improve or rehabilitate the fast voluntary motor response, especially for activities or sports that require it.

Does the Short Period of Resistance Training May Improve the Sleep Quality? Pilot Study

Purpose: The present study aimed evaluated the influence of exercise program on sleep quality of sedentary individuals. Methods: The study evaluated 30 subjects after resistance training session constituted by six multi-joints exercises (leg press, chest press, machine let pull down, seated machine shoulder press, crunches and machine trunk extension) three times a week for 40 days. The intensity of the effort was controlled using the follow criteria: the ideal repetitions for each set was between eight and fifteen. The Pittsburgh Sleep Quality Questionnaire (PSQI) was applied before and after training period. Results: There was a significant effect of short-term resistance training on all sub-scores of PSQI (p0.05). Conclusion: The resistance training program was able to improve the sleep quality in healthy subjects. In addition, the applicability of low-cost instruments (psychometric instruments like PSQI) to evaluate health parameters, which could be strengthened by other studies.

Effects of short-term resistance training and tapering on maximal strength, peak power, throwing ball velocity, and sprint performance in handball players.

The purpose of this study was to assess the effect of short-term resistance training and two weeks of tapering on physical performances in handball players. Following a ten-week progressive resistance training program, subjects were divided between an experimental (n = 10) and a control group (n = 10). The experimental group completed a resistance training program, followed by a two-week period when the training intensity was tapered by 60%, while the control group maintained their typical pattern of training. Muscle power (force–velocity test and squat and counter-movement jump tests), sprinting ability (10m and 30m), ability to change direction (T-half test) and throwing velocity (a 3-step throw with a run, and a jump throw) were evaluated before training, at the end of training and after tapering. The experimental group showed significantly larger interaction effects for the 10-week training period (12/15, 80%), than for the following 2 weeks of tapering (10/15, 67%), with the largest gains being in 15 m sprint times (d = 3.78) and maximal muscular strength in the snatch (d = 3.48). Although the performance of the experimental group generally continued to increase over tapering, the mean effect size for the training period was markedly higher (d = 1.92, range: 0.95–3.78) than that seen during tapering (d = 1.02, range: -0.17–2.09). Nevertheless the ten weeks of progressive resistance training followed by two weeks of tapering was an effective overall tactic to increase muscle power, sprint performance and ball throwing velocity in handball players.

Short-term Resistance Training Increases APPL1 Content in the Liver and the Insulin Sensitivity of Mice Fed a Long-term High-fat Diet.

APPL1, an adapter protein, interact directly with adiponectin receptors mediating adiponectin signaling and acting as a critical regulator of the crosstalk between adiponectin and insulin signaling pathway. The inadequate level of physical activity, high-calorie intake, or both lead to adverse consequences on health, like insulin resistance. On the order hand, physical exercise acts positively in the insulin action. Here, we investigated the effects of short-term resistance training (RT) on APPL1 content and adiponectin pathway in the liver of mice fed a long-term high-fat diet. Swiss mice were distributed into 3 groups: Mice that fed a chow diet (CTR); Mice fed a high-fat diet for 16 months (HFD); and mice fed a high-fat diet for 16 months and submitted to a climbing ladder exercise (RT) for 7 days (HFD-EXE). The results show that short-term RT increases the APPL1 content but wasn't able to alter AdipoR1 and AdipoR2 content in the liver of HFD-EXE mice. However, this increase in the APPL1 content in response to RT was accompanied by improvement in the insulin sensitivity. In summary, our data suggested that short-term RT improves glycemic homeostasis and increases APPL1 in the hepatic tissue of mice treated with long-term high-fat diet.

Effects of short-term resistance training on endothelial function and inflammation markers in elderly patients with type 2 diabetes: A randomized controlled trial.

To evaluate the effects of 12-weeks of strength training on endothelial function and inflammatory markers in elderly individuals with T2DM. Forty-four elderly patients with T2DM were screened for participation. After completion of the baseline assessment, participants were randomly assigned to either the resistance training group (RT) or an active control group (AC). Inflammatory (TNF-α, IL-6, IL-1β, IL-10 and CRP) and blood lipid profiles, glycated hemoglobin, basal artery diameter and flow mediated dilation were evaluated before and after the intervention. Comparisons between groups were obtained from the generalized estimation equation and all tests were two-tailed and the alpha level for significance set at 0.05. TNF-α and IL-1β were decreased in both groups, while no interactions were found for flow mediated dilation and basal artery diameter. No significant differences were found for blood lipid profile and glycated hemoglobin for both groups after the intervention period. No significant changes were found between the RT and AC groups, regarding inflammatory profile and endothelial function, which does not prove the superiority of this intervention model in the studied period.

Lower tendon stiffness in very old compared with old individuals is unaffected by short-term resistance training of skeletal muscle.

Aging negatively affects collagen-rich tissue, like tendons, but in vivo tendon mechanical properties and the influence of physical activity after the 8th decade of life remain to be determined. This study aimed to compare in vivo patellar tendon mechanical properties in moderately old (old) and very old adults and the effect of short-term resistance training. Twenty old (9 women, 11 men, >65 yr) and 30 very old (11 women, 19 men, >83 yr) adults were randomly allocated to heavy resistance training (HRT) or no training (CON) and underwent testing of in vivo patellar tendon (PT) mechanical properties and PT dimensions before and after a 3-mo intervention. Previous measurements of muscle properties, blood parameters, and physical activity level were included in the analysis. Data from 9 old HRT, 10 old CON, 14 very old CON, and 12 old HRT adults were analyzed. In addition to lower quadriceps muscle strength and cross-sectional area (CSA), we found lower PT stiffness and Young's modulus ( P < 0.001) and a trend toward the lower mid-portion PT-CSA ( P = 0.09) in very old compared with old subjects. Daily step count was also lower in very old subjects ( P < 0.001). Resistance training improved muscle strength and cross-sectional area equally in old and very old subjects ( P < 0.05) but did not affect PT mechanical properties or dimension. We conclude that PT material properties are reduced in very old age, and this may likely be explained by reduced physical activity. Three months of resistance training however, could not alter PT mechanical properties in very old individuals. NEW & NOTEWORTHY This research is the first to quantify in vivo tendon mechanical properties in a group of very old adults in their eighties. Patellar tendon stiffness was lower in very old (87 yr on average) compared with moderately old (68 yr on average) individuals. Reduced physical activity with aging may explain some of the loss in tendon stiffness, but regular heavy resistance training for 3 mo was not sufficient to change tendon mechanical properties.

The Effects of Short-Term Resistance Training with &amp; without Blood Flow Restriction on Neuromuscular Adaptations

The Effects of Short-Term Resistance Training with &amp; without Blood Flow Restriction on Neuromuscular Adaptations

Effects of Short-Term Free-Weight and Semiblock Periodization Resistance Training on Metabolic Syndrome.

South, MA, Layne, AS, Stuart, CA, Triplett, NT, Ramsey, MW, Howell, ME, Sands, WA, Mizuguchi, S, Hornsby, WG, Kavanaugh, AA, and Stone, MH. Effects of short-term free-weight and semiblock periodization resistance training on metabolic syndrome. J Strength Cond Res 30(10): 2682-2696, 2016-The effects of short-term resistance training on performance and health variables associated with prolonged sedentary lifestyle and metabolic syndrome (MS) were investigated. Resistance training may alter a number of health-related, physiological, and performance variables. As a result, resistance training can be used as a valuable tool in ameliorating the effects of a sedentary lifestyle including those associated with MS. Nineteen previously sedentary subjects (10 with MS and 9 with nonmetabolic syndrome [NMS]) underwent 8 weeks of supervised resistance training. Maximum strength was measured using an isometric midthigh pull and resulting force-time curve. Vertical jump height (JH) and power were measured using a force plate. The muscle cross-sectional area (CSA) and type were examined using muscle biopsy and standard analysis techniques. Aerobic power was measured on a cycle ergometer using a ParvoMedics 2400 Metabolic system. Endurance was measured as time to exhaustion on a cycle ergometer. After training, maximum isometric strength, JH, jump power, and V[Combining Dot Above]O2peak increased by approximately 10% (or more) in both the metabolic and NMS groups (both male and female subjects). Over 8 weeks of training, body mass did not change statistically, but percent body fat decreased in subjects with the MS and in women, and lean body mass increased in all groups (p ≤ 0.05). Few alterations were noted in the fiber type. Men had larger CSAs compared those of with women, and there was a fiber-specific trend toward hypertrophy over time. In summary, 8 weeks of semiblock free-weight resistance training improved several performance variables and some cardiovascular factors associated with MS.

Strength training improves muscle aerobic capacity and glucose tolerance in elderly

The primary aim of this study was to investigate the effect of short-term resistance training (RET) on mitochondrial protein content and glucose tolerance in elderly. Elderly women and men (age 71 ± 1, mean ± SEM) were assigned to a group performing 8 weeks of resistance training (RET, n = 12) or no training (CON, n = 9). The RET group increased in (i) knee extensor strength (concentric +11 ± 3%, eccentric +8 ± 3% and static +12 ± 3%), (ii) initial (0-30 ms) rate of force development (+52 ± 26%) and (iii) contents of proteins related to signaling of muscle protein synthesis (Akt +69 ± 20 and mammalian target of rapamycin +69 ± 32%). Muscle fiber type composition changed to a more oxidative profile in RET with increased amount of type IIa fibers (+26.9 ± 6.8%) and a trend for decreased amount of type IIx fibers (-16.4 ± 18.2%, P = 0.068). Mitochondrial proteins (OXPHOS complex II, IV, and citrate synthase) increased in RET by +30 ± 11%, +99 ± 31% and +29 ± 8%, respectively. RET resulted in improved oral glucose tolerance measured as reduced area under curve for glucose (-21 ± 26%) and reduced plasma glucose 2 h post-glucose intake (-14 ± 5%). In CON parameters were unchanged or impaired. In conclusion, short-term resistance training in elderly not only improves muscular strength, but results in robust increases in several parameters related to muscle aerobic capacity.

Muscle function and body composition profile in adolescents with restrictive anorexia nervosa: does resistance training help?

Purpose: The aim of this study was to analyze the effects of short-term resistance training on the body composition profile and muscle function in a group of Anorexia Nervosa restricting type (AN-R) patients. Methods: The sample consisted of AN-R female adolescents (12.8 ± 0.6 years) allocated into the control and intervention groups (n = 18 each). Body composition and relative strength were assessed at baseline, after 8 weeks and 4 weeks following the intervention. Results: Body mass index (BMI) increased throughout the study (p = 0.011). Significant skeletal muscle mass (SMM) gains were found in the intervention group (p = 0.045, d = 0.6) that correlated to the change in BMI (r = 0.51, p < 0.031). Meanwhile, fat mass (FM) gains were significant in the control group (p = 0.047, d = 0.6) and correlated (r > 0.60) with change in BMI in both the groups. Significant relative strength increases (p < 0.001) were found in the intervention group and were sustained over time. Conclusions: SMM gain is linked to an increased relative strength when resistance training is prescribed. Although FM, relative body fat (%BF), BMI and body weight (BW) are used to monitor nutritional progress. Based on our results, we suggest to monitor SMM and relative strength ratios for a better estimation of body composition profile and muscle function recovery.Implications for RehabilitationAnorexia Nervosa Restricting Type (AN-R)AN-R is a psychiatric disorder that has a major impact on muscle mass content and function. However, little or no attention has been paid to muscle recovery.High intensity resistance training is safe for AN-R after hospitalization and enhances the force generating capacity as well as muscle mass gains.Skeletal muscle mass content and muscular function improvements are partially maintained for a short period of time when the exercise program ceases.

Effects of Short-Term Resistance Training and Subsequent Detraining on Body and Thigh Composition

Effects of Short-Term Resistance Training and Subsequent Detraining on Body and Thigh Composition

Combining Normobaric Hypoxia With Short-term Resistance Training Has No Additive Beneficial Effect on Muscular Performance and Body Composition

The aim of this study was to determine the effects of short-term resistance training combined with systemic hypoxia on muscular performance and body composition. Eighteen resistance-untrained men (21.3 ± 2.0 years, 172.7 ± 5.5 cm, 67.3 ± 9.7 kg) were matched and assigned to 2 experimental groups: performing 6 weeks of squat exercise training under normobaric hypoxia (H, FiO2 = 15%) or normoxia (N). In both groups, subjects performed 3 weekly sessions (a total of 18 sessions) of 3 sets of back squat at 10-repetition maximum with 2 minutes of rest between sets. Dynamic, isometric, and isokinetic leg strength and body composition were measured under normoxia before and after resistance training. Squat 1 repetition maximum (1RM) improved significantly (p ≤ 0.05) after resistance training in both H and N groups (88.9 ± 16.9 to 109.4 ± 17.0 kg and 90.0 ± 12.2 to 105.6 ± 13.3 kg, respectively). However, there were no changes in maximal isometric and isokinetic leg strength, lean body mass, and fat mass after the resistance training in both groups. In addition, no significant differences were observed between H and N groups in squat 1RM, maximal isometric and isokinetic leg strength, and body composition. The major findings of this study suggest that short-term resistance training performed under normobaric hypoxia has no additive beneficial effect on muscular performance and body composition. In practical terms, our data suggest that the use of systemic hypoxia during short-term resistance training is not a viable method to further enhance muscular performance and body composition in previously resistance-untrained men.

Effects of short-term resistance training and pulsed electromagnetic fields on bone metabolism and joint function in severe haemophilia A patients with osteoporosis: a randomized controlled trial

Objectives: To assess the effects of short-term resistance training and pulsed electromagnetic fields on bone metabolism and joint function in patients with haemophilia with osteoporosis. Design: A randomized, controlled, patient and blood sample assessor-blinded, six-week trial, three times weekly. Setting: Hospital outpatients with severe haemophilia A and osteoporosis. Subjects: Forty-eight patients were randomly assigned to resistance training (RT, n = 13), combined resistance training with pulsed electromagnetic fields (RTPEMF, n = 12), pulsed electromagnetic fields (PEMF, n = 11) and control (n = 12) groups. Intervention: The RT group received 30–40 minutes of resistance exercises and placebo pulsed electromagnetic fields. The RTPEMF group received the same exercises with lower repetition and 30 minutes of pulsed electromagnetic fields. The PEMF group was exposed to 60 minutes of pulsed electromagnetic fields (30 Hz and 40 Gauss). Main measures: Bone-specific alkaline phosphatase, N-terminal telopeptide of type 1 collagen, and joint function, using the modified Colorado Questionnaire, were measured before and after the programme. Results: The absolute change of bone-specific alkaline phosphatase was significant in the RT and RTPEMF groups compared with the control group (25.41 ± 14.40, 15.09 ± 5.51, and −4.73 ± 2.93 U/L, respectively). The absolute changes in the total score for joint function were significant for knees, ankles, and elbows in the RT group (9.2 ± 1.38, 5.1 ± 0.5, and 3.2 ± 0.8, respectively) and the RTPEMF group (7.7 ± 1.0, 3.3 ± 0.6, and 2.5 ± 0.7, respectively) compared to the PEMF and control groups. This value was significant for knee joints in the PEMF group compared to the control group (3.4 ± 0.5 and 0.66 ± 0.4, respectively). Conclusions: Resistance training is effective for improving bone formation and joint function in severe haemophilia A patients with osteoporosis.

The Effect of Short-Term Resistance Training on Heart of Nonathletic Healthy Male Students by Echocardiograph

Background and Purpose: Resistance Training (RT) is known as weight or strength training. In response to this kind of training, both skeletal and cardiac muscles adapt. The purpose of the present study was to determine of effect of Short-term Resistance Training on Left Ventricular Structure of Nonathletic Healthy Male Students by Echocardiography. Methods and Materials: this quasi-experimental study involved thirty volunteer participants with an age range of 19to 25 years Mean ±SD:21.8±1.62.They were randomly divided into two groups of 15 (resistance training and control).Training program was performed 3 times a week for 12 weeks followed by 10 station with 50/. To 80/. With one repletion maximum (1RM).M and B-mode echocardiograph variable were measured at rest. The data were analyzed using dependant t-test and independent t–test. Result: Training caused a significant increase in the mean absolute and relative values of left ventricular mass (LVM), left ventricular end –diastolic dimensions (LVEDd), end-diastolic inter ventricular septum thickness (EDIVT)(P=0.000),and left ventricular posterior wall thickness end-diastolic (LVPWd)in the training group (p= 0.044 , p=0.00) Absolute and relative values of left ventricular end –systolic dimension (LVESd) decreased significantly after training (P=0.001, P=0.018).Between groups comparison of absolute and relative values of LVM, EDIVT and LVPWd in the training group showed a significant increases as compared with the control group (P=0.000):also there was a significant increase in the absolute value of LVEDd (P=0.002). Conclusion: Modification of resistance training can induce changes in the left ventricular structure of nonathletes.

The Effect of Short-Term Resistance Training on Hip and Knee Kinematics During Vertical Drop Jumps

The purpose of this study was to determine the effect of a weight-bearing free weight resistance training program alone on knee flexion, hip flexion, and knee valgus during unilateral and bilateral drop jump tasks. Twenty-nine young adult females with previous athletic experience were randomly divided into a control (n = 16) and a resistance training (n = 13) groups. The resistance training group completed 8 weeks of lower extremity, weight-bearing exercises using free weights, whereas the control group did not train. A pre- and posttest was conducted to measure knee valgus, knee flexion, and hip flexion during unilateral (30 cm) and bilateral (60 cm) vertical drop jumps for maximum height. Joint angles were determined using 3-dimensional electromagnetic tracking sensors (MotionMonitor; Innovative Sports Training, Inc., Chicago, IL, USA). Initial training intensity for the bilateral squat was 50% of the subject's 1 repetition maximum (RM), which increased 5% each week to 85% during the final week. Sets and repetitions ranged from 2 to 4 and from 4 to 12, respectively. The training loads for all other exercises (lunge, step-up, unilateral squat, and Romanian deadlift) increased from 15RM to 6RM from the initial to the final week. A repeated measures analysis of variance was used to determine differences in the hip and knee joint angles. No significant differences for knee valgus and hip flexion measures were found between the groups after training; however, knee flexion angle significantly increased in the training group from the pretest (77.2 ± 4.1°) to posttest (83.2 ± 3.7°) during the bilateral drop jump. No significant changes occurred during the unilateral drop jump. Bilateral measures for knee flexion, hip flexion, and knee valgus were significantly (p < 0.05) greater than the unilateral measures during the drop jump task, which indicate an increased risk for anterior cruciate ligament (ACL) injury during unilateral drop jumps. The data support that the strength and conditioning specialist can implement resistance training alone during a short-term training period to reduce the risk of ACL injury by increasing knee flexion during a bilateral drop jump task. Increased knee flexion angles after resistance training may indicate a reduced risk for knee injury from improved neuromuscular control, resulting in a softer landing.

Effects of Short-Term Resistance Training on Serum Leptin Levels in Obese Adolescents

The purpose of this study was to examine the effects of a short-term resistance training program on serum leptin concentrations in obese adolescents. Eighteen Chinese obese adolescents participated in the supervised weight management program. Resistance training was conducted three times a week on alternate days for 6 weeks. Body composition [body fat mass (FM) and body lean mass (LM)] determined by dual-energy X-ray absorptiometry, muscle strength and leptin, insulin and glucose were measured before and after training. Subjects demonstrated significantly improved strength of leg, chest and bicep under conditions of stability in weight, FM and LM. There were positive correlations between leptin and body mass index, FM, %FM, waist girth and hip girth, and negative correlations between leptin and %L M at the resting state before and after 6 weeks of resistance training. No significant relationship was found between leptin concentration and the parameters of muscular strength or concentrations of insulin and glucose. Compared to pre-training values, serum leptin levels were not significantly altered, while relative leptin (leptin/FM) decreased significantly after the short-term resistance training. These results indicate that short-term resistance training enhances muscle strength but does not alter leptin levels in obese adolescents with weight and FM stability. The results also suggest that 6 weeks of resistance training decreases the requirement of leptin per unit of FM and improves leptin sensitivity in obese adolescents.

Throwing performance after resistance training and detraining

The purpose of the present study was to investigate the effect of short-term resistance training and detraining on shot put throwing performance. Eleven young healthy subjects with basic shot put skills participated in 14 weeks of resistance training, which was followed by 4 weeks of detraining. Shot put performance in four field tests was measured before (T1) and after (T2) resistance training and after detraining (T3). At the same time points, one repetition maximum (1RM) was measured in squat, bench press, and leg press. Fat-free mass (FFM) was determined with dual x-ray absorptiometry and muscle biopsies obtained from vastus lateralis for the determination of fiber type composition and cross-sectional area (CSA). 1RM strength increased 22-34% (p < 0.01) at T2 and decreased 4-5% (not significantly different) at T3. Shot put performance increased 6-12% (p < 0.05) after training and remained unaltered after detraining. FFM increased at T2 (p < 0.05) but remained unchanged between T2 and T3. Muscle fiber CSA increased 12-18% (p < 0.05) at T2. Type I muscle fiber CSA was not altered after detraining, but type IIa and IIx fiber CSA was reduced 10-12% (p < 0.05). The percentage of type IIx muscle fibers was reduced after training (T1 = 18.7 +/- 4, T2 = 10.4 +/- 1; p < 0.05), and it was increased at T3 compared with T2 (T3 = 13.7 +/- 1; p < 0.05). These results suggest that shot put performance remains unaltered after 4 weeks of complete detraining in moderately resistance-trained subjects. This might be linked to the concomitant reduction of muscle fiber CSA and increase in the percentage of type IIx muscle fibers.

Age-Related Changes in Skeletal Muscle Activation Following Short-Term Resistance Training

PURPOSE: To determine the effects of short-term resistance training on measures of muscular strength and skeletal muscle activation of the triceps surae in adult males from 20-79 years of age. METHODS: Forty-six subjects volunteered for this study and were designated into one of three groups, classified as individuals aged between 20-39 years (GI, n=20), 40-59 years (GII, n=16), and 60-79 years (GIII, n=10). Subjects participated in three supervised resistance training sessions over the course of seven days, performing four lower body exercises during each training session. Subjects were assessed for muscle cross-sectional area (CSA), maximal isometric strength (ISO), antagonist co-activation (ANTCO), and muscle activation determined through twitch interpolation (VA%) and surface electromyography (SEMG). Two-way repeated measures ANOVA was used to determine group differences and changes with training. RESULTS: Analysis of baseline data revealed a significant difference (p=0.007) in ISO between GI (127.9 ± 5.5 nm) and GIII (99.8 ± 7.5 nm) for plantarflexion maximal strength. No significant differences (p>0.05) were observed for CSA, ANTCO, VA%, or SEMG between groups. Following training, there was no significant change (p>0.05) in CSA, ISO, ANTCO, or VA% for any age group. Examination of SEMG data determined significant main effects for muscle group (p=0.001) and time (p=0.013) for amplitude. A significant decrease for the time main effect (p=0.001) in SEMG median frequency was also observed post-training. CONCLUSIONS: The results from the present study indicated that there were no significant pre-test to post-test changes in muscle size, muscular strength, antagonist co-activation, or muscle activation following the experimental training period for any group. These findings were unlike those from previous investigations of the leg extensors that have reported improvements in neuromuscular performance after only two or three training sessions. This data may be useful for those involved in rehabilitative programs suggesting the muscles of the lower limb could require more than three training sessions to elicit the neuromuscular adaptations that typically occur during the early stages of a resistance training program.