Heavy Resistance Strength Training Research Articles

Effects of Equal Volume Heavy-Resistance Strength Training Versus Strength Endurance Training on Physical Fitness and Sport-Specific Performance in Young Elite Female Rowers.

Strength training is an important means for performance development in young rowers. The purpose of this study was to examine the effects of a 9-week equal volume heavy-resistance strength training (HRST) versus strength endurance training (SET) in addition to regular rowing training on primary (e.g., maximal strength/power) and secondary outcomes (e.g., balance) in young rowers. Twenty-six female elite adolescent rowers were assigned to an HRST (n = 12; age: 13.2 ± 0.5 yrs; maturity-offset: +2.0 ± 0.5 yrs) or a SET group (n = 14; age: 13.1 ± 0.5 yrs; maturity-offset: +2.1 ± 0.5 yrs). HRST and SET comprised lower- (i.e., leg press/knee flexion/extension), upper-limbs (i.e., bench press/pull; lat-pull down), and complex exercises (i.e., rowing ergometer). HRST performed four sets with 12 repetitions per set at an intensity of 75–95% of the one-repetition maximum (1-RM). SET conducted four sets with 30 repetitions per set at 50–60% of the 1-RM. Training volume was matched for overall repetitions × intensity × training per week. Pre-post training, tests were performed for the assessment of primary [i.e., maximal strength (e.g., bench pull/knee flexion/extension 1-RM/isometric handgrip test), muscle power (e.g., medicine-ball push test, triple hop, drop jump, and countermovement jump), anaerobic endurance (400-m run), sport-specific performance (700-m rowing ergometer trial)] and secondary outcomes [dynamic balance (Y-balance test), change-of-direction (CoD) speed (multistage shuttle-run test)]. Adherence rate was >87% and one athlete of each group dropped out. Overall, 24 athletes completed the study and no test or training-related injuries occurred. Significant group × time interactions were observed for maximal strength, muscle power, anaerobic endurance, CoD speed, and sport-specific performance (p ≤ 0.05; 0.45 ≤ d ≤ 1.11). Post hoc analyses indicated larger gains in maximal strength and muscle power following HRST (p ≤ 0.05; 1.81 ≤ d ≤ 3.58) compared with SET (p ≤ 0.05; 1.04 ≤ d ≤ 2.30). Furthermore, SET (p ≤ 0.01; d = 2.08) resulted in larger gains in sport-specific performance compared with HRST (p < 0.05; d = 1.3). Only HRST produced significant pre-post improvements for anaerobic endurance and CoD speed (p ≤ 0.05; 1.84 ≤ d ≤ 4.76). In conclusion, HRST in addition to regular rowing training was more effective than SET to improve selected measures of physical fitness (i.e., maximal strength, muscle power, anaerobic endurance, and CoD speed) and SET was more effective than HRST to enhance sport-specific performance gains in female elite young rowers.

The effects of different exercise training modalities on plasma proenkephalin Peptide F in women

Due to the important interactions of proenkephalin fragments (e.g., proenkephalin [107–140] Peptide F) to enhance activation of immune cells and potentially combat pain associated with exercise-induced muscle tissue damage, we examined the differential plasma responses of Peptide F to different exercise training programs. Participants were tested pre-training (T1), and after 8 weeks (T2) of training. Fifty-nine healthy women were matched and then randomly assigned to one of four groups: heavy resistance strength training (STR, n=18), high intensity endurance training (END, n=14), combined strength and endurance training (CMB, n=17), or control (CON, n=10). Blood was collected using a cannula inserted into a superficial vein in the antecubital fossa with samples collected at rest and immediately after an acute bout of 6 X 10 RM in a squat resistance exercise before training and after training. Prior to any training, no significant differences were observed for any of the groups before or after acute exercise. With training, significant (P≤0.95) elevations were observed with acute exercise in each of the exercise training groups and this effect was significantly greater in the CMB group. These data indicate that in untrained women exercise training will not change resting of plasma Peptide F concentrations unless both forms of exercise are performed but will result in significant increases in the immediate post-exercise responses. Such findings appear to indicate adrenal medullary adaptations opioid production significantly altered with exercise training.

Brain connectivity aberrations in anabolic-androgenic steroid users.

Sustained anabolic-androgenic steroid (AAS) use has adverse behavioral consequences, including aggression, violence and impulsivity. Candidate mechanisms include disruptions of brain networks with high concentrations of androgen receptors and critically involved in emotional and cognitive regulation. Here, we tested the effects of AAS on resting-state functional brain connectivity in the largest sample of AAS-users to date. We collected resting-state functional magnetic resonance imaging (fMRI) data from 151 males engaged in heavy resistance strength training. 50 users tested positive for AAS based on the testosterone to epitestosterone (T/E) ratio and doping substances in urine. 16 previous users and 59 controls tested negative. We estimated brain network nodes and their time-series using ICA and dual regression and defined connectivity matrices as the between-node partial correlations. In line with the emotional and behavioral consequences of AAS, current users exhibited reduced functional connectivity between key nodes involved in emotional and cognitive regulation, in particular reduced connectivity between the amygdala and default-mode network (DMN) and between the dorsal attention network (DAN) and a frontal node encompassing the superior and inferior frontal gyri (SFG/IFG) and the anterior cingulate cortex (ACC), with further reductions as a function of dependency, lifetime exposure, and cycle state (on/off).

Rate of force development: physiological and methodological considerations.

The evaluation of rate of force development during rapid contractions has recently become quite popular for characterising explosive strength of athletes, elderly individuals and patients. The main aims of this narrative review are to describe the neuromuscular determinants of rate of force development and to discuss various methodological considerations inherent to its evaluation for research and clinical purposes. Rate of force development (1) seems to be mainly determined by the capacity to produce maximal voluntary activation in the early phase of an explosive contraction (first 50–75 ms), particularly as a result of increased motor unit discharge rate; (2) can be improved by both explosive-type and heavy-resistance strength training in different subject populations, mainly through an improvement in rapid muscle activation; (3) is quite difficult to evaluate in a valid and reliable way. Therefore, we provide evidence-based practical recommendations for rational quantification of rate of force development in both laboratory and clinical settings.

Effects of heavy-resistance strength and balance training on unilateral and bilateral leg strength performance in old adults.

The term “bilateral deficit” (BLD) has been used to describe a reduction in performance during bilateral contractions when compared to the sum of identical unilateral contractions. In old age, maximal isometric force production (MIF) decreases and BLD increases indicating the need for training interventions to mitigate this impact in seniors. In a cross-sectional approach, we examined age-related differences in MIF and BLD in young (age: 20–30 years) and old adults (age: >65 years). In addition, a randomized-controlled trial was conducted to investigate training-specific effects of resistance vs. balance training on MIF and BLD of the leg extensors in old adults. Subjects were randomly assigned to resistance training (n = 19), balance training (n = 14), or a control group (n = 20). Bilateral heavy-resistance training for the lower extremities was performed for 13 weeks (3 × / week) at 80% of the one repetition maximum. Balance training was conducted using predominately unilateral exercises on wobble boards, soft mats, and uneven surfaces for the same duration. Pre- and post-tests included uni- and bilateral measurements of maximal isometric leg extension force. At baseline, young subjects outperformed older adults in uni- and bilateral MIF (all p < .001; d = 2.61–3.37) and in measures of BLD (p < .001; d = 2.04). We also found significant increases in uni- and bilateral MIF after resistance training (all p < .001, d = 1.8-5.7) and balance training (all p < .05, d = 1.3-3.2). In addition, BLD decreased following resistance (p < .001, d = 3.4) and balance training (p < .001, d = 2.6). It can be concluded that both training regimens resulted in increased MIF and decreased BLD of the leg extensors (HRT-group more than BAL-group), almost reaching the levels of young adults.

The effects of exercise training programs on plasma concentrations of proenkephalin Peptide F and catecholamines

To determine if exercise training alters the pattern and magnitude of plasma concentrations of proenkephalin Peptide F and epinephrine, plasma proenkephalin [107–140] Peptide Fir and catecholamines were examined pre-training (T-1), and after 4- (T-2), 8- (T-3), and 12-weeks (T-4) of training. 26 healthy men were matched and randomly assigned to one of three groups: heavy resistance strength training (Strength, n=9), high intensity endurance training (Endurance, n=8), or both training modalities combined (Combined, n=9). Blood was collected using a syringe with a cannula inserted into a superficial arm vein with samples collected at rest, after each 7min stage and 5 and 15min into recovery. With training, all groups observed shifted plasma Peptide F responses to graded exercise, where significant increases were observed at lower exercise intensities. Increases in plasma epinephrine with exercise were observed in all groups. The Combined group saw increases at 25% at T-3 and for 50% at T-2, T-3, and T-4 which was higher than T-1. The Endurance group demonstrated increases for 50% at T-1, T-2, T-3 but not at T-4. The plasma epinephrine response to graded exercise was reduced in the Strength group. Increases in plasma norepinephrine above rest were observed starting at 50% ▪. The Strength group demonstrated a significant reduction in norepinephrine observed at 100% at T-3 and T-4. Peptide F and catecholamines responses to graded exercise can be altered by different types of physical exercise training. Simultaneous high intensity training may produce adrenal medulla exhaustion when compared to single mode training.

The Use of Eccentric Strength Training to Enhance Maximal Muscle Strength, Explosive Force (RDF) and Muscular Power - Consequences for Athletic Performance

Heavy-resistance strength training results in marked increases in maximal muscle strength and power in both athletes, untrained subjects and elderly individuals. The addition of eccentric overload training (loads > 100% 1RM) appears to evoke enhanced gains in these parameters. Further, the use of plyometric training evokes marked increases in maximal muscle power. The adaptive physiological mechanisms involve changes in neuromuscular activity and alterations in muscle morphology (fiber size, fiber lengths) and muscle architecture, respectively, while changes in tendon stiffness may potentially contribute as well.

The effect of strength training, recreational soccer and running exercise on stretch–shortening cycle muscle performance during countermovement jumping

The purpose of the present study was to evaluate the effect of contrasting training modalities on mechanical muscle performance and neuromuscular activity during maximal SSC (stretch–shortening cycle) countermovement jumps (CMJ). Bilateral countermovement jumping, surface electromyography (EMG) and muscle fiber size (CSA) were studied in untrained individuals (n=49, 21–45yrs) pre and post 12weeks of progressive heavy-resistance strength training (ST, n=8), recreational soccer training (SOC, n=15), high-intensity interval running (INT, n=7), continuous running (RUN, n=9) or continuation of an inactive life-style (CON, n=10). ST displayed shortened CMJ take-off time (p<.05) and increased (p<.05) maximal CMJ jump height, peak down- and upward velocity of center of mass (COM), rate of vertical force development (RFD: ΔFZ/Δt), peak power production, rate of power development (RPD), mean plantar flexor EMG and peak hamstring rate of EMG rise (RER). Peak quadriceps EMG rate of rise increased in SOC (p<.05). Moreover, ST and SOC demonstrated increased quadriceps muscle fiber CSA and lean leg mass. Positive relationships (r>.70) were observed following ST between training-induced changes in CMJ SSC muscle performance, neuromuscular activity and muscle fiber CSA, respectively. ST induced a more rapid CMJ take-off phase and elevated muscle power production, indicating a more explosive-type SSC muscle performance. No effects were detected in CMJ performance after continuous running, high-intensity interval running and recreational soccer, despite an increased muscle fiber CSA and quadriceps muscle activity in SOC. Enhanced neuromuscular activity in the hip extensors (hamstrings) and plantar flexors, and increased myofiber fiber size were responsible for the enhanced CMJ SSC muscle performance with ST.

Explosive-type Heavy-resistance Strength Training Leads To Improved Postural Stability in 60 And 80-yr Old Women

Aging is associated with a progressive impairment in postural balance control, which results in an increased incidence of falls at old age. Specifically, a reduced rapid force capacity (rate of force development, RFD) of the lower limb muscles results in an impaired ability to reverse a fall during sudden stumbling. We recently showed that explosive-type heavy-resistance strength training (HRT) elicits increased RFD in old (60 yr) and very old (80 yr) women. However, the effect on postural stability remains unknown. PURPOSE: To examine the effect of explosive-type HRT on postural stability in old and very old women. METHODS: Old (62.7 ± 2.2 yrs, n=17, TG60) and very old (81.8 ± 2.7, n=10, TG80) women performed 12 wks of explosive-type HRT for the leg muscles (24 sessions) using 75-80% 1-RM loads. Non-training age-matched women served as controls (n=17, CG60; n=12, CG80). Center of pressure (CoP) excursion was analyzed during 60-s bilateral static stance using force plate analysis (Kistler 9281B) and average values were obtained in the final 15-s epoc. Data were normalized to individual base of support (BoS) dimensions. RESULTS: Prior to training 80-yr women demonstrated 32%, 102% and 42% greater CoP sway length (L), sway area (A) and velocity-moment (VM), respectively, than 60-yr women. Post training TG60 showed decreased A (-21%) and VM (-28%) (p<0.01), while L tended to decrease by 8% (p=0.108). CG60 showed no changes, and % pre-to-post changes were greater (p<0.05) in TG60 than CG60 for all parameters. Post training changes in TG80 for A (-18%), VM (-7%) and L (-2%) failed to reach statistical significance, however % pre-to-post changes for A were greater in TG80 than CG80 (p<0.05). A similar tendency emerged for L and VM (p=0.103-0.108). M-L CoP variability (SD[CoPx]) decreased 23% in TG60 along with 28% reduced VM variability (p<0.01). Likewise, A-P VM variability tended to decrease in TG80 (p=0.089) after HRT. CONCLUSION: When contrasted to age-matched sedentary controls, explosive-type resistance training led to improved postural stability in women aged 60 and 80 years, respectively. However, within-group changes were less manifest in 80-yr old individuals, suggesting that HRT should be supplemented with specific postural balance exercise to more effectively improve postural stability in very old individuals.

Effects of strength training on endurance capacity in top‐level endurance athletes

The effect of concurrent strength (S) and endurance (E) training on adaptive changes in aerobic capacity, endurance performance, maximal muscle strength and muscle morphology is equivocal. Some data suggest an attenuated cardiovascular and musculoskeletal response to combined E and S training, while other data show unimpaired or even superior adaptation compared with either training regime alone. However, the effect of concurrent S and E training only rarely has been examined in top-level endurance athletes. This review describes the effect of concurrent SE training on short-term and long-term endurance performance in endurance-trained subjects, ranging from moderately trained individuals to elite top-level athletes. It is concluded that strength training can lead to enhanced long-term (>30 min) and short-term (<15 min) endurance capacity both in well-trained individuals and highly trained top-level endurance athletes, especially with the use of high-volume, heavy-resistance strength training protocols. The enhancement in endurance capacity appears to involve training-induced increases in the proportion of type IIA muscle fibers as well as gains in maximal muscle strength (MVC) and rapid force characteristics (rate of force development), while likely also involving enhancements in neuromuscular function.

Follow up of some anthropometric and ergometric parameters during 8 week resistance training

Muscle cell adaptation to physical activity is well known. Hypertrophy is one of the basic changes but metabolic changes are following the anatomic ones as well. The aim of the study was to follow up the changes of the ergometric parameters and surface area of the thigh muscles evoked by the heavy resistance strength training. The study included 15 male subjects, who took part in the heavy resistance strength training lasting 8 weeks. Anthropometric (surface area of the thigh muscles) and ergometric (peak power) parameters were measured at the beginning and at the end of the 8 week period in order to evaluate the changes in the thigh muscles. The surface area of the thigh muscles increased significantly (p < 0.05) (the left leg 9.26 +/- 10.32 cm2 and the right leg 9.07 +/- 0.57 cm2). Metabolic changes were assessed via Wingate test and also showed significant increase (p < 0.05). This finding indirectly indicates the increase in anaerobic capacity of the trained muscles. The heavy resistance training evidently influenced the changes in the trained muscles. After the 8 week period both antropometric and metabolic changes were evident, and significant.

Effect of Aging on Power Output and Functional Reflex Activity

Only a few studies have been conducted concerning the effects of aging on explosive force production capacity and on functional reflex activity (FRA). PURPOSE: Therefore, the purpose of this study was to investigate the impact of aging on (a) rate of force development (RFD) during maximal isometric leg extension force (MIF), (b) the first 30ms of the force-time curve (FTC) during MIF, and (c) on the ability to compensate for gait perturbations (GP). METHODS: 28 healthy young (Y) (n=14, age 27±3.1yrs, BMI=23.6±0.8kg/m2) and old men (O) (n=14, age 67.3±3.7yrs, BMI=25.5±2.1kg/m2) volunteered as subjects in this study. All subjects were tested for: (a) treadmill deceleration impulses at a walking speed of 3.5km/h, and (b) their MIF and RFD on a leg-press. RFDmax was defined as the maximal slope at deflection of the FTC. RFD30 was calculated as the mean slope of the FTC over the time interval 0-30ms. EMG activity was recorded from M. tibialis (TI) and M. vastus medialis (VM) of the right leg using surface electrodes. The analysed time interval for GP was 120ms after the first physiological response in the goniometer signal. Integrated and time normalized EMG (mean amplitude Voltage (MAV)) of TI during GP was normalized on the swing phase of a regular gait cycle. For MIF, MAV was analysed in the time interval 0-30ms and normalized on MAV of VM 100ms pre and post MIF. RESULTS: MIF, RFDmax and RFD30 were significantly reduced in O compared to Y (MIF: 1307±83 vs. 2390±103N, p<.01; RFDmax: 9.2±1.3 vs. 18.4±1.2N/ms, p<.01; RFD30: 0.28±0.06 vs. 1.66±0.21N/ms, p<.01). Normalized MAV of VM in the time interval 0-30ms was decreased in O compared to Y (84.5±30.8 vs. 95.5±56.6%, n.s.). For GP, latency of TI was enhanced in O compared to Y (77.7±3.6 vs. 75.1±2.5ms, n.s.). Normalized MAV of TI during GP was significantly reduced in O compared to Y (216±66 vs. 306±145%, p<.05). However, no correlation could be found between MAV of TI during GP and MIF, RFDmax and RFD30. DISCUSSION: Aging leads to tremendous decreases in MIF, RFD and FRA, with RFD being more affected than MIF. Heavy resistance strength training seems to be a wellsuited method to counteract age related decreases in MIF and RFD. Furthermore, there is evidence that balance training has the potential to enhance FRA even in old age (1).

Explosive-type Strength Training in the Elderly

The age-related decline in muscle power and explosive force capacity (i.e. contractile rate of force development RFD) is as stronger predictor for incidence of falling, motor impairment, self-reported functional status and balance capability in community-dwelling old adults than maximal muscle strength per se. It was therefore recently suggested to develop strength training programmes aimed at maximising maximal muscle power and RFD by implementing explosive concentric movements with training loads of 40–60% of 1RM. However, older individuals often perform weight-bearing motor tasks close to their maximum capability (i.e. 1RM) and above especially during unexpected tasks such as reversing an impending fall. PURPOSE: To investigate the effect of 12-week, twice a week, heavy-resistance strength training (75–80 % of 1RM) with fast-to-explosive execution of the movements on maximal voluntary contraction (MVC), explosive force characteristics (RFD and impulse), muscle power and functional performances in two age-groups of community-dwelling elderly women (TG60, TG80, age-groups 60 and 80, respectively). METHODS: Elderly women from two age-groups, 60 (62.7 2.2 years, n=40) and 80 (81.8 2.7 years, n=25) were randomized (matched) into two training and two control groups (TG60, n=20; TG80, n=12) (CG 60, n=20; CG80, n=13). MVC, RFD and impulse were obtained during a maximal isometric unilateral leg press manuevre. Mechanical performance was assessed as jump height, (JH) and peak power (Ppeak) in a standardized countermovement jump (CMJ) and as mean power (Prigmean). in the Nottingham single-legged power rig. Functional motor performances were i) five-repeated chair rise, ii) 10-m walking test at self selected and maximal speed, and iii) Physical Performance Test (PPT). RESULTS: RFD, impulse, MVC, P peak', JH and Prigmean increased with training in both age-groups. The gains in RFD (50.5%), impulse (41.9%) and MVC (28.1%) for TG 80 were of such a magnitude that the difference observed pre intervention with the age-group 60 was abolished after training. Chair-rise and PPT improved in TG80 and only chair rise in TG60, whereas no improvements occurred in self-selected and maximal 10-meter gait speed. CONCLUSIONS: The present findings indicate that heavy-resistance strength training performed with explosive movement characteristics is highly effective in inducing adaptive neuromuscular changes in selected physiological variables and functional performances commonly associated with risk of falls and disability in aged individuals. This training modality seems to be safe and suitable for healthy women even in the 8th decade of life.

Age and sex affect human muscle fibre adaptations to heavy‐resistance strength training

This study assessed age and sex effects on muscle fibre adaptations to heavy-resistance strength training (ST). Twenty-two young men and women (20-30 years old) and 18 older men and women (65-75 years old) completed 9 weeks of heavy-resistance knee extension exercises with the dominant leg 3 days week(-1); the non-dominant leg served as a within-subject, untrained control. Bilateral vastus lateralis muscle biopsies were obtained before and after ST for analysis of type I, IIa and IIx muscle fibre cross-sectional area (CSA) and fibre type distribution. One-repetition maximum (1-RM) strength was also assessed before and after ST. ST resulted in increased CSA of type I, IIa and IIx muscle fibres in the trained leg of young men, type I and IIa fibres in young women, type IIa fibres in older men, and type IIx fibres in older women (all P<0.05). Analysis of fibre type distribution revealed a significant increase in the percentage of type I fibres (P<0.05) along with a decrease in type IIx fibres (P=0.054) after ST only in young women. There were no significant changes in muscle fibre CSA or fibre type distribution in the untrained leg for any group. All groups displayed significant increases in 1-RM (27-39%; all P<0.01). In summary, ST led to significant increases in 1-RM and type II fibre CSA in all groups; however, age and sex influence specific muscle fibre subtype responses to ST.

Myostatin gene expression is reduced in humans with heavy-resistance strength training: a brief communication.

This study examined changes in myostatin gene expression in response to strength training (ST). Fifteen young and older men (n = 7) and women (n = 8) completed a 9-week heavy-resistance unilateral knee extension ST program. Muscle biopsies were obtained from the dominant vastus lateralis before and after ST. In addition to myostatin mRNA levels, muscle volume and strength were measured. Total RNA was reverse transcribed into cDNA, and myostatin mRNA was quantified using quantitative PCR by standard fluorescent chemistries and was normalized to 18S rRNA levels. A 37% decrease in myostatin expression was observed in response to ST in all subjects combined (2.70 +/- 0.36 vs 1.69 +/- 0.18 U, arbitrary units; P < 0.05). Though the decline in myostatin expression was similar regardless of age or gender, the small number of subjects in these subgroups suggests that this observation needs to be confirmed. No significant correlations were observed between myostatin expression and any muscle strength or volume measure. Although further work is necessary to clarify the findings, these data demonstrate that myostatin mRNA levels are reduced in response to heavy-resistance ST in humans.

HEAVY RESISTANCE STRENGTH TRAINING IMPROVES CARDIOVASCULAR RESPONSES TO WEIGHT LOADED WALKING IN CARDIAC REHABILITATION PARTICIPANTS

Moderate to heavy levels of strength training have been shown to improve muscular strength individuals with cardiovascular disease. However, data is sparse concerning the effects of heavy resistance strength training (HRST) on cardiovascular responses to activities of daily living in this population. PURPOSE To examine the effects of HRST on 1RM strength and cardiovascular responses to weight loaded walk testing (WLWT) in male (n=21; 65 ± 7 yr; 92 ± 16 kg) and female (n=12; 67 ± 8 yr; 74 ± 8 kg) Phase III/IV Cardiac Rehabilitation Participants. METHODS After baseline testing, subjects performed either one set or two sets of whole body HRST twice per week for eight weeks (ST; n=20). Each set of HRST began with a 5 RM resistance, and was gradually lowered until 10 repetitions could be completed. Heart rate (HR), blood pressure (BP), rate-pressure product (RPP), oxygen saturation (O2 sat), and rating of perceived exertion (RPE) were assessed during individualized, incremental WLWT before and after HRST. WLWT data for the ST group were compared to a control group (CON; n=13) performing eight weeks of aerobic training only. RESULTS Significant increases in 1 RM were observed for all exercises after HRST regardless of training volume (all p < 0.001). The ST group displayed lower systolic BP responses to the first three stages of WLWT (all p < 0.05) after HRST, while RPP was lower during stages one, two, and four (all p ≤ 0.05). HRST did not induce significant changes in O2 sat or RPE during WLWT in the ST group. In comparison, there were no significant changes in the CON group for any variable measured during WLWT over a similar time span. CONCLUSIONS These data suggest that one set of HRST is as effective as two sets for improving muscular strength and cardiovascular responses to WLWT in individuals with cardiovascular disease.

Acute effect of alternating heavy and light resistances on power output during upper-body complex power training.

This study investigated the effect on upper-body power output of manipulating resistances during contrast or complex power training. This power-training strategy typically entails the athlete alternating sets of a heavy resistance in a strength-oriented exercise with sets of lighter resistances in a power-oriented exercise. Sixteen rugby league players, who were experienced in power training and who performed complex training on a regular basis, served as subjects for this study and were divided equally into a control (Con) or experimental (Exp) group. Both groups were pre- and posttested for power output while performing explosive bench press throws in a Smith machine with a resistance of 50 kg (BT P50). The Exp group performed an intervention strategy of a 6-repetition set of bench presses with a resistance of 65% of 1 repetition maximum (65% 1RM) between tests. At the pretest occasion, no differences were observed between the groups in power output; however, at the posttesting, a significant difference in power output was observed between the groups in the BT P50. The 4.5% increase in the power output recorded during the posttesting BT P50 for the Exp group was determined to be significantly different from all other scores (p < or = 0.05). These data indicate that the performance of a set of heavy resistance strength training exercise between power training sets will acutely enhance power output in the second power training set. This effect has been previously theorized as possibly due to some combination of acute neural or mechanical adaptations.

Increased rate of force development and neural drive of human skeletal muscle following resistance training.

The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.

EFFECTS OF HEAVY RESISTANCE TRAINING ON MUSCLE PROFILE, STRENGTH AND SOCCER PERFORMANCE IN FEMALE ELITE SOCCER PLAYERS.

PURPOSE: The aim of the present study was to evaluate the effect of heavy resistance training on maximal and ‘explosive' muscle strength, soccer performance and muscle morphology of female elite soccer players. METHODS: 16 players were tested at end of autumn season (P1), after 12 weeks of either isolated heavy resistance training (1.7 sessions/wk) (HRT) or detraining (CO) (P2), and at end of the following spring season (P3). Isokinetic eccentric and concentric strength was measured in a Kincom. Explosive strength was determined as the contractile Rate of Force Development (RFD) in maximal isometric contraction. Sprint, countermovement jump, and kicking performance were measured. Histochemical analyses were performed to identify fibre type composition and fibre area (type I, IIA and IIX). Non-parametric tests were used for statistical analyses. RESULTS: At P2, the HRT group increased maximal eccentric quadriceps muscle strength and RFD (p < 0.05). A significant decrease in RFD of the hamstrings was observed in the CO group (p < 0.05). At P2, an increase in percentage of type IIA fibres with a corresponding decrease in type IIX fibres were observed for the HRT group (p < 0.05). Fibre area of type IIA and IIX increased in the HRT group, and the fibre area of type IIX decreased in the CO group (p < 0.05). The HRT group improved jump, sprint and kicking performance significantly at P3. CONCLUSIONS: Heavy resistance strength training induced significant increases in maximal eccentric and explosive quadriceps strength. Soccer performance improved only when resistance training was followed by a period of soccer training. Strength increases were accompanied by fibre type transformation from IIX towards IIA and hypertrophy of type IIA and IIX muscle fibres. 12 weeks of detraining induced a significant decrease in RFD of the hamstrings in the CO group. A decrease in RFD of the hamstrings could be a potential risk factor for knee injury in fast and explosive movements.

NEURAL ADAPTATION TO RESISTANCE TRAINING EVIDENCED BY CHANGES IN EVOKED V-WAVE AND H REFLEX RESPONSES

The Hoffmann (H) reflex can be used to assess the excitability of spinal α-motoneurons and the degree of presynaptic inhibition of Ia afferent neurons during maximal muscle contraction. The V wave reflects the magnitude of neural motor output from the α-motoneuron pool when activated via central descending pathways (Upton et al. 1971). PURPOSE: To examine neural adaptation mechanisms induced by resistance training using combined V wave and H reflex measurements. METHODS: Evoked H reflex and V wave responses were recorded in the soleus muscle of 14 male subjects before and after 14 weeks of heavy-resistance strength training (38 sessions). The H reflex was superimposed onto maximal isometric plantar flexion by electrically stimulating the tibial nerve (1 ms square pulse) at an intensity that elicited M wave responses of 0.2Mmax. In addition, in separate trials of maximal isometric plantar flexion the tibial nerve was stimulated at supramaximal intensities to elicit a V wave (Vmax) and maximal M wave (Mmax). Muscle strength was measured as maximal concentric and eccentric isokinetic plantar-flexor moments (KinCom, 30 s−1). RESULTS: The V wave amplitude (V/Mmax) increased from 0.308 ± 0.048 to 0.478 ± 0.034 mV with training (± SEM; p < 0.01) while Mmax remained unchanged (10.78 ± 0.86, 10.21 ± 0.66 mV). The H reflex amplitude increased from 5.37 ± 0.41 to 6.24 ± 0.49 mV (p < 0.05). Maximal concentric and eccentric muscle strength increased from 112.2 ± 16.7 to 137.6 ± 10.8 Nm and 135.5 ± 18.6 to 175.6 ± 8.2 Nm, respectively (p < 0.05). CONCLUSIONS: Evoked V wave and H reflex responses increased following training (55% and 16%, respectively), indicating an enhanced motor output of spinal motoneurons during maximal voluntary muscle contraction. Taken together, these data indicate that the training induced increase in motoneuron output may involve both supraspinal and spinal adaptation mechanisms (i.e. increased central motor drive, elevated motoneuron excitability and/or reduced presynaptic inhibition).