What phenomena do occur in blood flow-restricted muscle?

Blood flow restriction training does not negatively alter the mechanical strength or histomorphology of uninjured equine superficial digital flexor tendons

BACKGROUND

Low load exercise training with blood flow restriction (BFR) has become increasingly used by human physical therapists to prescribe controlled exercise following orthopaedic injury; its effects on the equine superficial digital flexor tendon (SDFT), however, are unknown.

OBJECTIVE

To investigate outcomes of pressure specific BFR walking exercise on uninjured equine SDFT biomechanics and histomorphology.

STUDY DESIGN

Controlled in vivo experiment.

METHODS

Four forelimbs of four horses were exposed to 40 BFR-walk sessions (10-min interval walking) on a treadmill over a 56-day study period with their contralateral forelimbs serving as untreated controls. Similarly, four forelimbs of four control horses were exposed to 40 sham cuff walk sessions. On study Day 56, all horses (n = 8) were humanely euthanised and forelimb SDFTs underwent non-destructive biomechanical testing and corresponding histomorphological analysis. Significance in biomechanical parameters between treatment groups was analysed using a mixed-effects ANOVA with Tukey's post-hoc tests.

RESULTS

Statistically significant differences in SDFT stiffness for both first (p = 0.02) and last cycles (p = 0.03) were appreciated within the BFR treated group only, with BFR exposed forelimbs being significantly stiffer than the contralateral unexposed forelimbs. When normalised to cross-sectional area, no significant differences were appreciated among treatment groups in elastic modulus for the first (p = 0.5) or last cycles (p = 0.4). No histological differences were appreciated among treatment groups according to Bonar, Movin, or musculotendinous junction evaluation criteria.

MAIN LIMITATIONS

Short-term comparisons were performed in a small sample population without correlation to performance outcome measures. Optimal occlusion percentages and walk protocols remain unknown.

CONCLUSIONS

This study demonstrated no negative impact of BFR on mechanical strength of the equine SDFT; however, evidence suggests that BFR results in increased tendon stiffness based on biomechanical testing and subsequent calculations. No consistent detrimental histomorphological changes were seen.

Inter-set rest configuration effect on acute physiological and performance-related responses to a resistance training session in terrestrial vs simulated hypoxia

Background

Metabolic stress is considered a key factor in the activation of hypertrophy mechanisms which seems to be potentiated under hypoxic conditions.This study aimed to analyze the combined effect of the type of acute hypoxia (terrestrial vs simulated) and of the inter-set rest configuration (60 vs 120 s) during a hypertrophic resistance training (RT) session on physiological, perceptual and muscle performance markers.

Methods

Sixteen active men were randomized into two groups based on the type of hypoxia (hypobaric hypoxia, HH: 2,320 m asl; vs normobaric hypoxia, NH: FiO2 of 15.9%). Each participant completed in a randomly counterbalanced order the same RT session in four separated occasions: two under normoxia and two under the corresponding hypoxia condition at each prescribed inter-set rest period. Volume-load (load × set × repetition) was calculated for each training session. Muscle oxygenation (SmO2) of the vastus lateralis was quantified during the back squat exercise. Heart rate (HR) was monitored during training and over the ensuing 30-min post-exercise period. Maximal blood lactate concentration (maxLac) and rating of perceived exertion (RPE) were determined after the exercise and at the end of the recovery period.

Results

Volume-load achieved was similar in all environmental conditions and inter-set rest period length did not appreciably affect it. Shorter inter-set rest periods displayed moderate increases in maxLac, HR and RPE responses in all conditions. Compared to HH, NH showed a moderate reduction in the inter-set rest-HR (ES > 0.80), maxLac (ES > 1.01) and SmO2 (ES > 0.79) at both rest intervals.

Conclusions

Results suggest that the reduction in inter-set rest intervals from 120 s to 60 s provide a more potent perceptual, cardiovascular and metabolic stimulus in all environmental conditions, which could maximize hypertrophic adaptations in longer periods of training. The abrupt exposure to a reduced FiO2 at NH seems to reduce the inter-set recovery capacity during a traditional hypertrophy RT session, at least during a single acute exposition. These results cannot be extrapolated to longer training periods.

Resistance Training in Hypoxia as a New Therapeutic Modality for Sarcopenia-A Narrative Review

Hypoxic training is believed to be generally useful for improving exercise performance in various athletes. Nowadays, exercise intervention in hypoxia is recognized as a new therapeutic modality for health promotion and disease prevention or treatment based on the lower mortality and prevalence of people living in high-altitude environments than those living in low-altitude environments. Recently, resistance training in hypoxia (RTH), a new therapeutic modality combining hypoxia and resistance exercise, has been attempted to improve muscle hypertrophy and muscle function. RTH is known to induce greater muscle size, lean mass, increased muscle strength and endurance, bodily function, and angiogenesis of skeletal muscles than traditional resistance exercise. Therefore, we examined previous studies to understand the clinical and physiological aspects of sarcopenia and RTH for muscular function and hypertrophy. However, few investigations have examined the combined effects of hypoxic stress and resistance exercise, and as such, it is difficult to make recommendations for implementing universal RTH programs for sarcopenia based on current understanding. It should also be acknowledged that a number of mechanisms proposed to facilitate the augmented response to RTH remain poorly understood, particularly the role of metabolic, hormonal, and intracellular signaling pathways. Further RTH intervention studies considering various exercise parameters (e.g., load, recovery time between sets, hypoxic dose, and intervention period) are strongly recommended to reinforce knowledge about the adaptational processes and the effects of this type of resistance training for sarcopenia in older people.

Muscle fibre activation and fatigue with low-load blood flow restricted resistance exercise-An integrative physiology review

Blood flow-restricted resistance exercise (BFRRE) has been shown to induce increases in muscle size and strength, and continues to generate interest from both clinical and basic research points of view. The low loads employed, typically 20%-50% of the one repetition maximum, make BFRRE an attractive training modality for individuals who may not tolerate high musculoskeletal forces (eg, selected clinical patient groups such as frail old adults and patients recovering from sports injury) and/or for highly trained athletes who have reached a plateau in muscle mass and strength. It has been proposed that achieving a high degree of muscle fibre recruitment is important for inducing muscle hypertrophy with BFRRE, and the available evidence suggest that fatiguing low-load exercise during ischemic conditions can recruit both slow (type I) and fast (type II) muscle fibres. Nevertheless, closer scrutiny reveals that type II fibre activation in BFRRE has to date largely been inferred using indirect methods such as electromyography and magnetic resonance spectroscopy, while only rarely addressed using more direct methods such as measurements of glycogen stores and phosphocreatine levels in muscle fibres. Hence, considerable uncertainity exists about the specific pattern of muscle fibre activation during BFRRE. Therefore, the purpose of this narrative review was (1) to summarize the evidence on muscle fibre recruitment during BFRRE as revealed by various methods employed for determining muscle fibre usage during exercise, and (2) to discuss reported findings in light of the specific advantages and limitations associated with these methods.

Altitude-induced effects on muscular metabolic stress and hypertrophy-related factors after a resistance training session

This study examined the acute effects of exposure to moderate altitude on factors associated with muscular adaptations following whole-body hypertrophy-oriented resistance training (R _T) sessions. Thirteen resistance-trained males completed both counterbalanced standard hypertrophic R _T sessions (3 sets × 10RM, 2 min rest) at moderate-altitude (H; 2320 m asl) and under normoxic conditions (N; <700 m asl). Participants rested 72 h between training sessions. Before and after the exercise session, blood samples were obtained for determination of metabolites and ions (lactate, inorganic phosphate, liquid carbon dioxide and calcium) and hormones (testosterone and growth hormone). Session-related performance and perception of effort (s-RPE) were also monitored. Results showed no meaningful differences in performance or s-RPE (8.5 ± 1.4 vs 8.6 ± 0.8 respectively for N and H; p = 0.603). All blood variables displayed statistically significant changes throughout the recovery period compared to basal levels (p < 0.05), except for the testosterone. However, no altitude effect was observed in maximal blood lactate, calcium or anabolic hormones (p > 0.05). The reduction observed in the liquid carbon dioxide concentration in H (21.11 ± 1.46 vs 16.19 ± 1.61 mmol·l^-1) seems compatible with an increase in buffering capacity. Compared to N, inorganic phosphate displayed lower recovery values after the R _T in H (2.89 ± 0.64 vs 2.23 ± 0.60 mg dl^-1; p = 0.007). The results of this study do not support an accentuated effect of acute moderate terrestrial hypoxia on metabolic and hormonal factors linked to muscle growth during hypertrophic resistance training.

Mean Propulsive Velocity Is a Viable Method for Adjusting the Resistance-Training Load at Moderate Altitude

We examined the viability of using mean propulsive velocity (MPV) to adjust the load in the countermovement jump (CMJ) at moderate altitude. Twenty-four volunteers were assigned to a 4-week power-oriented resistance training (R_T) program in either normoxia (N, 690 m) or intermittent hypobaric hypoxia (IH, 2,320 m). The load was adjusted to maintain execution velocity of CMJ at 1m·s^-1 of MPV. Relative peak power output (P_rel), and percentage of velocity loss throughout the sets (VL) were determined for each session. The internal load was measured by the rating of perceived exertion (RPE). The absolute load lifted was higher in IH compared to N (75.6 ± 8.4 vs. 58.5 ± 12.3 kg P < 0.001). However, similar relative increases for both groups were found when comparing the final values (IH: 8.2%, P = 0.007; N: 9.8%, P = 0.03) with no changes in VL between groups (P = 0.36). Post-study P_rel improved significantly only in IH (+7% W·kg^-1, P = 0.002). Mean RPE was greater in IH vs. N (6.8 ± 1.5 vs. 5.6 ± 2, P < 0.001). The MPV seems to be a viable method for adjusting external load during R_T at moderate altitude. However, given that R_T at moderate altitude increases RPE, it is prudent to monitor internal load when using the MPV to best determine the actual physiological stress of the session.

Strengthening the Brain-Is Resistance Training with Blood Flow Restriction an Effective Strategy for Cognitive Improvement?

Aging is accompanied by a decrease in physical capabilities (e.g., strength loss) and cognitive decline. The observed bidirectional relationship between physical activity and brain health suggests that physical activities could be beneficial to maintain and improve brain functioning (e.g., cognitive performance). However, the exercise type (e.g., resistance training, endurance training) and their exercise variables (e.g., load, duration, frequency) for an effective physical activity that optimally enhance cognitive performance are still unknown. There is growing evidence that resistance training induces substantial brain changes which contribute to improved cognitive functions. A relative new method in the field of resistance training is blood flow restriction training (BFR). While resistance training with BFR is widely studied in the context of muscular performance, this training strategy also induces an activation of signaling pathways associated with neuroplasticity and cognitive functions. Based on this, it seems reasonable to hypothesize that resistance training with BFR is a promising new strategy to boost the effectiveness of resistance training interventions regarding cognitive performance. To support our hypothesis, we provide rationales of possible adaptation processes induced by resistance training with BFR. Furthermore, we outline recommendations for future studies planning to investigate the effects of resistance training with BFR on cognition.

Effects of two programs of metabolic resistance training on strength and hypertrophy

Abstract Introduction: The effects of low intensity resistance training combined with vascular occlusion have been investigated by several studies. Similar results on strength and hypertrophy have been observed when such method was compared to high intensity protocols. However, due to the specific apparatus needed to apply vascular occlusion (ex.: Kaatsu) on some exercises, alternative forms of metabolic training might be used. In the present study, an isometric contraction was performed within each concentric-eccentric transition phase, for every repetition, to elicit metabolic stress. Objective: The aim of the present study was to analyze the effects of two resistance training protocols with metabolic characteristics on strength (1MR), circumference (CIRC) and muscle thickness (measured with ultrasonography [MT]). Subjective perception of discomfort was also recorded with an analogical-visual pain scale (AVP). Methods: Twelve young, healthy men were trained with two different methods during 10 weeks. The right limb was trained with an isometric contraction within each concentric-eccentric transition phases for every repetition (ISO) whereas the left limb was trained with a pneumatic cuff to apply vascular occlusion (OC) on the knee extensor muscles. Both methods were trained at 20% 1MR. Results: It was observed increases on medial tight CIRC, proximal MT, medial MT, distal MT and 1MR, with no difference between both methods. The perception of discomfort was greater for ISO at the end of the third set and lower than reported by OC, at the beginning and end of the training program. Conclusions: Both protocols produced similar gains on strength and hypertrophy. The advantages of training with low loads are important to elderly or rehabilitation training programs. Other studies that compare this method with conventional resistance training are warranted.

Hypoxia and resistance exercise: a comparison of localized and systemic methods

It is generally believed that optimal hypertrophic and strength gains are induced through moderate- or high-intensity resistance training, equivalent to at least 60% of an individual's 1-repetition maximum (1RM). However, recent evidence suggests that similar adaptations are facilitated when low-intensity resistance exercise (~20-50% 1RM) is combined with blood flow restriction (BFR) to the working muscles. Although the mechanisms underpinning these responses are not yet firmly established, it appears that localized hypoxia created by BFR may provide an anabolic stimulus by enhancing the metabolic and endocrine response, and increase cellular swelling and signalling function following resistance exercise. Moreover, BFR has also been demonstrated to increase type II muscle fibre recruitment during exercise. However, inappropriate implementation of BFR can result in detrimental effects, including petechial haemorrhage and dizziness. Furthermore, as BFR is limited to the limbs, the muscles of the trunk are unable to be trained under localized hypoxia. More recently, the use of systemic hypoxia via hypoxic chambers and devices has been investigated as a novel way to stimulate similar physiological responses to resistance training as BFR techniques. While little evidence is available, reports indicate that beneficial adaptations, similar to those induced by BFR, are possible using these methods. The use of systemic hypoxia allows large groups to train concurrently within a hypoxic chamber using multi-joint exercises. However, further scientific research is required to fully understand the mechanisms that cause augmented muscular changes during resistance exercise with a localized or systemic hypoxic stimulus.

Effects of blood flow restriction duration on muscle activation and microvascular oxygenation during low-volume isometric exercise

The purpose of the investigation was to observe how varying occlusion durations affected neuromuscular activation and microvascular oxygenation during low-volume isometric knee extension exercise. Healthy, recreationally active males performed isometric knee extension at a variety of submaximal intensities under different blood flow restriction (BFR) occlusion durations. The occlusion pressure (130% SBP) was applied either 5 min prior to exercise (PO), immediately prior to exercise (IO) or not during exercise (CON). Surface electromyography (sEMG) and near-infrared spectroscopy (NIRS) was used to record the neuromuscular activation and microvascular oxygenation of the knee extensors during exercise. No difference in sEMG was observed in the vastus lateralis or vastus medialis during any exercise condition or any submaximal intensity. PO elicited greater microvascular deoxygenation (deoxy-[Hb + Mb]) compared to CON (P≤0·05) at all submaximal intensities and also compared to IO at 20% maximal voluntary contraction (MVC). IO resulted in a greater deoxy-[Hb + Mb] response during low-intensity exercise (20% and 40% MVC) compared to CON (P≤0·05). These findings suggest that applying BFR 5 min before exercise can enhance the exercise-induced metabolic stress (i.e. deoxy-[Hb + Mb]), measured via NIRS, during low-intensity exercise (20% MVC) compared to applying BFR immediately prior to exercise. Furthermore, the increased metabolic stress observed during IO is attenuated during high-intensity (60% MVC, 80% MVC) exercise when compared to CON conditions. Knowledge of the changes in exercise-induced metabolic stress between the various occlusion durations may assist in developing efficient BFR exercise programmes.

Neuromuscular and metabolic responses to three different resistance exercise methods

PURPOSE

The aim of this study was to compare the effect of resistance exercise with three different methods on integrated electromyography (IEMG) and metabolic responses in recreational athletes.

METHODS

Twenty four males (mean 23.59±0.87 years) were randomly assigned to three experimental groups. Participants performed knee extension exercises: Slow (SL: 3-3, 3s for each concentric and eccentric action with 50% of 1 RM), Normal (NH: 1-1, 1 s for each concentric and eccentric action 80% of 1 RM) and Traditional (TH: 2-4, 2s for concentric and 4s for eccentric action with 80% of 1 RM). Plasma lactate, glucose and triglyceride concentration and IEMG was measured before and immediately after performing four sets of resistance exercise.

RESULTS

Each method significantly decreased IEMG (P<0.05), but there was no significant difference between groups. Lactate was increased following TH and NH more than SL method (P<0.05). Each method significantly increased plasma glucose (P<0.05). Work considering time under tension (workTUT) was higher (P<0.05) during TH method than the other methods and during SL it was higher than NH method (P<0.05). Volume load was higher (P<0.05) during NH than the other two methods and during TH it was higher than SL method (P<0.05).

CONCLUSION

These results indicate that exercise intensity during the resistance exercise is important for the enhancement of lactate responses, but the slow resistance exercise method could induce acute neuromuscular response as much as high intensity methods. It seems that this method will be advantageous for those who want to increase acute neuromuscular changes with low exercise intensity and volume.

Time course of regional vascular adaptations to low load resistance training with blood flow restriction

Distortion to hemodynamic and ischemic stimuli during blood flow restriction (BFR) exercise may influence regional vascular adaptation. We examined changes at the conduit, resistance, and capillary level in response to low load resistance exercise with BFR. Eleven males (22 ± 3 yr, 178 ± 4 cm, 78 ± 9 kg) completed 6 wk (3 days/wk) unilateral plantar flexion training with BFR at 30% 1 repetition maximum (1-RM). The contralateral leg acted as a nonexercised control (CON). Popliteal artery function [flow-mediated dilation, FMD%] and structure [maximal diameter] and resistance vessel structure [peak reactive hyperemia] were assessed using Doppler ultrasound before and at 2-wk intervals. Calf filtration capacity was assessed using venous occlusion plethysmography before and after training. BFR training elicited an early increase in peak reactive hyperemia (1,400 ± 278 vs. 1,716 ± 362 ml/min at 0 vs. 2 wk; t-test: P = 0.047), a transient improvement in popliteal FMD% (5.0 ± 2.1, 7.6 ± 2.9, 6.6 ± 2.1, 5.7 ± 1.6% at 0, 2, 4 and 6 wk, respectively; ANOVA: P = 0.002), and an increase in maximum diameter (6.06 ± 0.44 vs. 6.26 ± 0.39 mm at 0 vs. 6 wk; Bonferroni t-test: P = 0.048). Capillary filtration increased after 6 wk BFR training (P = 0.043). No changes in the CON leg were observed. Adaptation occurred at all levels of the vascular tree in response to low load resistance exercise with BFR. Enhanced peak reactive hyperemia and transient improvement in popliteal artery function occurred before changes in artery structural capacity.

Brachial artery modifications to blood flow-restricted handgrip training and detraining

Low load resistance training with blood flow restriction (BFR) can increase muscle size and strength, but the implications on the conduit artery are uncertain. We examined the effects of low-load dynamic handgrip training with and without BFR, and detraining, on measures of brachial artery function and structure. Nine male participants (26 ± 4 yr, 178 ± 3 cm, 78 ± 10 kg) completed 4 wk (3 days/wk) of dynamic handgrip training at 40% 1 repetition maximum (1RM). In a counterbalanced manner, one forearm trained under BFR (occlusion cuff at 80 mmHg) and the other under nonrestricted (CON) conditions. Brachial artery function [flow-mediated dilation (FMD)] and structure (diameter) were assessed using Doppler ultrasound. Measurements were made before training (pretraining), after training (posttraining), and after 2-wk no training (detraining). Brachial artery diameter at rest, in response to 5-min ischemia (peak diameter), and ischemic exercise (maximal diameter) increased by 3.0%, 2.4%, and 3.1%, respectively, after BFR training but not after CON. FMD did not change at any time point in either arm. Vascular measures in the BFR arm returned to baseline after 2 wk detraining with no change after CON. The data demonstrate that dynamic low-load handgrip training with BFR induced transient adaptations to conduit artery structure but not function.

Venous blood gas and metabolite response to low-intensity muscle contractions with external limb compression

The effect of low-intensity resistance exercise with external limb compression (100 [EC100] and 160 [EC160] mm Hg) on limb blood flow and venous blood gas-metabolite response was investigated and compared with that of high-intensity resistance exercise (no external compression). Unilateral elbow flexion muscle contractions were performed at 20% (75 repetitions, 4 sets, 30-second rest intervals) and 70% of 1-repetition maximum (1-RM; 3 sets, each set was until failure, 3-minute rest intervals). Precontraction brachial arterial blood flow (Doppler ultrasound) was reduced with EC100 or EC160 (56% and 39% of baseline value, respectively) compared with no external compression (control). At 20% 1-RM, brachial arterial blood flow increased after contractions performed with EC160 (190%), but not with the others. Decreases in venous oxygen partial pressure (P(v)O(2)) and venous oxygen saturation (S(v)O(2)) were greater during EC100 and EC160 than control (mean [SE]: P(v)O(2), 28 [3] vs 26 [2] vs 33 [2] mm Hg; S(v)O(2), 41% [5%] vs 34% [4%] vs 52% [5%], respectively). Changes in venous pH (pH(v)), venous carbon dioxide partial pressure (P(v)CO(2)), and venous lactate concentration ([L(-)](v)) were greater with EC160 than EC100 and/or control (pH(v), 7.19 [0.01] vs 7.25 [0.01] vs 7.27 [0.02]; P(v)CO(2), 72 [3] vs 64 [2] vs 60 [3] mm Hg; [L(-)](v), 5.4 [0.6] vs 3.7 [0.4] vs 3.0 [0.4] mmol/L, respectively). Seventy percent 1-RM contractions resulted in greater changes in pH(v) (7.14 [0.02]), P(v)CO(2) (91 [5] mm Hg), and [L(-)](v) (7.0 [0.5] mmol/L) than EC100 and EC160, but P(v)O(2) (30 [4] mm Hg) and S(v)O(2) (40% [3%]) were similar. In conclusion, changes in pH(v), P(v)CO(2), and [L(-)](v), but not in P(v)O(2) and S(v)O(2), are sensitive to changes in relative, "internal" intensity of low-intensity muscle contractions caused by reduced blood flow (EC160) or high-intensity muscle contractions. Given the magnitude of the changes in pH(v), P(v)CO(2), and [L(-)](v), it appears plausible that they may be involved in stimulating the observed increase in muscle activation via group III and IV afferents.

Muscle, tendon, and somatotropin responses to the restriction of muscle blood flow induced by KAATSU-walk training

OBJECTIVE

The efficacy of KAATSU training has been demonstrated in human athletes, both as a therapeutic method as well as a training aid. The purpose of this study was to investigate the effects of slow walk training combined with restriction of muscle blood flow (KAATSU) on muscle and tendon size.

METHODS

Six healthy, unfit Standardbred mares performed walking (240 m/min for 10 min and then 5 min recovery) with KAATSU, and 6 mares performed walking without KAATSU. A specially designed elastic cuff1 was placed at the most proximal position of the forelegs and inflated to a pressure of 200-230 mmHg throughout the walking and recovery sessions. The training was conducted once a day, 6 days/week for 2 weeks. Skeletal muscle thickness and tendon thickness were measured using B-mode ultrasound at baseline and after 2 weeks of training. Venous blood samples were obtained before the first acute exercise and 5, 15 and 60 min afterwards. Serum somatotropin concentration was determined using a commercially available equine-specific ELISA kit.

RESULTS

The acute increase in plasma somatotropin was 40% greater (P<0.05) in the KAATSU-walk group than in the Control-walk group 5 min after exercise and remained elevated (P<0.05) at 15 and 60 min post exercise compared with the Control-walk group. After 2 weeks of training, muscle thickness increased (P<0.05) 3.5% in the KAATSU-walk group but did not change in the Control-walk group (0.7%). Tendon thickness did not change (P>0.05) in either group.

CONCLUSIONS

These data demonstrate that KAATSU training can induce muscle hypertrophy in horses and suggest that KAATSU training may provide significant therapeutic/ rehabilitative value in horses, as has been shown in man.

Time under Tension and Blood Lactate Response during Four Different Resistance Training Methods

Mechanical stimuli have often been suggested to be the major determinant of resistance training adaptations; however, some studies suggested that metabolic changes also play an important role in the gains of muscle size and strength. Several resistance training methods (RTM) have been employed with the purpose of manipulating mechanical and metabolic stimuli; however, information about their physiological effects are scarce. The objective of this study was to compare the time under tension (TUT) and blood lactate responses among four different RTM reported in the literature. The four RTM were performed in a knee extension machine at 10 repetition maximum (RM) load by 12 recreationally trained young men. The RTM tested were: 10RM, super-slow (SL-subjects performed one 60-second repetition with 30 seconds for eccentric and 30 seconds for concentric phase), functional isometrics (FI-in each repetition, a five-second maximal isometric contraction was executed with the knees fully extended) and adapted vascular occlusion (VO-subjects performed a 20-second maximal isometric contraction with the knees fully extended and immediately proceeded to normal isoinertial lifts). According to the results, all RTM produced significant increases in blood lactate levels. However, blood lactate responses during FI (4.48+/-1.57 mM) and VO (4.23+/-1.66 mM) methods were higher than the SL method (3.41+/-1.14 mM). The TUT for SL (60 s), FI (56.33+/-6.46 s), and VO (53.08+/-4.76 s) methods were higher than TUT for 10RM (42.08+/-3.18 s). Additionally, TUT for the SL method was higher than TUT during the VO method. Therefore, the SL method may not be recommended if one wants to provide a high metabolic stimulus. The FI method appeared to be especially effective in promoting both type of stimuli.