Far-infrared-emitting fabric improves neuromuscular performance of knee extensor.

The aim of this study was to verify if exposure to the far-IR emitted by fabric (FIR) is able to improve the neuromuscular performance of the knee extensors of resistance-trained males regardless of changes of the temperature. It is a crossover, randomized, double-blind, and placebo-controlled trial. Fourteen resistance-trained males (age: 24.3 ± 4 years; body mass: 82.8 ± 11.3 kg; height: 176.3 ± 4.2 cm) were randomly assigned to one of initial conditions: FIR (n = 7) or placebo (n = 7). After 4 days, the participants were submitted to neuromuscular tests in an isokinetic dynamometer (maximal isometric voluntary contraction (MVC) and fatigue test). After a week of washout, participants performed the other condition. We measured peak torque (Nm), total work (J), fatigue index (%), root mean square (mV), median frequency (Hz), and temperature (°C) of thigh. The FIR was worn for 82 ± 19 h before the experimental session, totaling 317 ± 74 kJ of energy irradiation. There was a significant increase (p < 0.05) for pre-MVC (318.5 ± 68.7 Nm) and post-MVC (284.1 ± 58.2 Nm), and a trend (p = 0.055) for significant increase for total work (4,122.2 ± 699.8 J) on FIR condition regardless of none change on temperature and electromyographic (EMG) signals. FIR improved the neuromuscular performance of knee extensors in resistance-trained males regardless of changes on temperature and EMG. The present results suggest that the FIR could optimize the neuromuscular performance with 82 ± 19 h of wear.

Does Varying Repetition Tempo in a Single-Joint Lower Body Exercise Augment Muscle Size and Strength in Resistance-Trained Men?

ABSTRACT: Pearson, J, Wadhi, T, Barakat, C, Aube, D, Schoenfeld, BJ, Andersen, JC, Barroso, R, Ugrinowitsch, C, and De Souza, EO. Does varying repetition tempo in a single-joint lower body exercise augment muscle size and strength in resistance-trained men? J Strength Cond Res 36(8): 2162-2168, 2022-This study compared the effects of FAST and SLOW eccentric repetition tempo in a single exercise volume-matched intervention on muscle thickness (MT) and strength in resistance-trained men. Using a within-subject design, 13 subjects had each leg randomly assigned to SLOW (1-0-3) or FAST (1-0-1) repetition tempo. Subjects underwent an 8-week strength-training (ST) intervention performed twice weekly. Unilateral leg-extension one repetition-maximum (1RM) and anterior thigh MT at the proximal (MTP) and distal (MTD) portions were assessed via ultrasound imaging at baseline and after 8 weeks of RT. Rating of perceived exertion (RPE) assessments of the training sessions (i.e., 16 per leg) were averaged for further analysis. Both legs similarly increased MTP (estimated differences: FAST: 0.24 cm, 3.6%; SLOW: 0.20 cm, 3.1%). However, for MTD, analysis of covariance analysis showed a leg effect ( p = 0.02) in which absolute pre-to-post change was greater in FAST compared with SLOW (estimated differences: FAST 0.23 cm, 5.5%; SLOW: 0.13 cm, 2.2%). For 1RM, both legs similarly increased maximum strength (estimated differences: FAST: 9.1 kg, 17.0%; SLOW: 10.4 kg, 22.1%, p ≤ 0.0001). The SLOW group had a higher RPE than FAST (8.59 vs. 7.98, p = 0.002). Despite differences in RPE, our results indicate that both repetition tempos produced similar muscular adaptations. However, they also suggest that the FAST tempo may provide a small hypertrophic advantage at the distal quadriceps. From a practical standpoint, strength and conditioning professionals may implement a FAST tempo at least in one single-joint exercise during an 8-week training period to enhance regional hypertrophic adaptations in trained individuals.

How do swimmers pace the 400 m freestyle and what affects the pacing pattern?

To describe the pacing pattern of elite 400 m freestyle swimmers, understand how athletes select the first half compared to their 200-m race pace, and correlate critical speed (CS) and D' with pacing parameters. The best all-time 400 m performances were obtained, and 200 m performances were retrieved from the same competition. Twenty-four performances were selected and, when possible, 50 m-splits were obtained. CS and D' were calculated based on the 200 m and 400 m performances. Most athletes adopted a parabolic pacing pattern. Performance in the 400 m correlated with that of the 200 m (rho = 0.418, p = 0.042), the % difference between 200 m performance and 200 m split correlated with CS (rho = -0.595, p = 0.002) and with D' (rho = 0.808, p < 0.001). The correlation between D' and % difference between average speed and CS was nearly perfect (rho = 1.000, p < 0.001). Recommendations of having the first half of the 400 m 4-5 s slower than their 200 m race do not seem to be appropriate for all swimmers and depends on physiological abilities.

Is stronger better? Influence of a strength phase followed by a hypertrophy phase on muscular adaptations in resistance-trained men.

Although used by resistance-trained individuals, it is unknown if increasing muscle strength prior to hypertrophy training leads to greater muscle growth and strength gains. We investigated muscle thickness and maximum strength in 26 resistance-trained men who were randomly assigned to either: STHT, consisted in a 3-week strength-oriented training period (4x1-3 repetition maximum [RM]) prior to a 5-week hypertrophy-oriented period (4x8-12RM), or HT, which comprised an 8-week hypertrophy-oriented training period. Vastus lateralis muscle thickness, and back squat and leg-press 1-RM were assessed at pre, third week, and after 8 weeks of training. When pre-to-post changes are compared, STHT induced greater muscle growth (p = 0.049; 95%CI = 0.15-3.2%; d = 0.81) and strength gains in the back squat (p = 0.015; 95%CI = 1.5-13%; d = 1.05) and leg-press 45° (p = 0.044; 95%CI = 0.16-9.9%; d = 0.79) compared to HT. Our results support the use of a period to increase muscle strength prior to an HT to increase muscle thickness and maximum strength in resistance-trained men.

Does a 4-week training period with hand paddles affect front-crawl swimming performance?

This study investigated the effects of a 4-week training with hand paddles (HPD) on front-crawl swimming performance (SP), clean swimming speed (SPEED), stroke rate (SR), stroke length (SL) and tethered force (TF). Twenty swimmers (10 men and 10 women) were paired according to performance and gender, and were randomly assigned to control (CON, 22.4 ± 2.3 years) or HPD (21.8 ± 1.9 years) groups. During 4 weeks both groups performed the same training, except for a sprint training set (3 times/week, 10 × 10 strokes all-out, 1-min rest) completed with (HPD = 320 cm2) and without (CON) paddles. Afterwards, both groups performed the same training over a 2-week taper period. SP, SPEED, SR, SL and TF were assessed before (PRE) and after the 4-week period (POST), after the first (T1) and second taper weeks (T2). Swimmers rated their perceived exertion for the sprint training set (RPETS) and the training session for determining internal training load (ITL). SP, SPEED, SR, SL and TF did not change from PRE to POST, T1 and T2. ITL and RPETS were not different between groups. Training 4 weeks with HPD does not affect swimming performance, so the use of HPD remains unsupported in such period.

Ischemic Preconditioning Improves Strength Endurance Performance.

Carvalho, L and Barroso, R. Ischemic preconditioning improves strength endurance performance. J Strength Cond Res 33(12): 3332-3337, 2019-Ischemic preconditioning (IPC) has been used to improve performances in aerobic and anaerobic activities. However, a few studies aimed at observing the effects of IPC on resistance training. The purpose of this study is to examine the effects of IPC on the number of repetitions performed during high-load resistance training. We also aimed at investigating blood lactate concentration and muscle activation in an attempt to understand the physiological mechanisms that may be caused by IPC. Ten resistance-trained participants performed four 5-minute cycles of either IPC (250 mm Hg) or Placebo (10 mm Hg) before performing a single set to failure of knee extension exercise with 85% of 1 repetition maximum. We also assessed muscle activation during the set (EMGRMS), median power frequency (EMGMPF), and blood lactate concentration before, 3, 7, and 11 minutes after (peak value was identified and used to calculate delta to prevalues, Δlactate). Data are presented as mean, 90% confidence intervals (CIs), and were analyzed with paired t-test. The level of significance was set at p < 0.05. Participants performed on average 3.9 repetitions (90% CI = 2.4-5.4; p = 0.01), which is ∼20%, more in the IPC condition. There were no significant differences between IPC and Placebo for EMGMPF (5.0%; 90% CI = -5.2 to 15; p = 0.50), EMGRMS (4.5%; 90% CI = -8.8 to 17; p = 0.78), and Δlactate (44%; 90% CI = 11-144; p = 0.16). Our results demonstrate the effect of IPC just on the number of repetitions performed in high-load resistance exercise compared with the Placebo condition.

Blood flow restriction increases metabolic stress but decreases muscle activation during high-load resistance exercise.

INTRODUCTION: We investigated differences in metabolic stress (lactate) and muscle activation (electromyography; EMG) when high-load resistance exercise (HL) is compared with a condition in which blood flow restriction (BFR) is applied during the exercise or during the rest interval. METHODS: Twelve participants performed HL with BFR during the intervals (BFR-I), during the set (BFR-S), and without BFR. Each condition consisted of 3 sets of 8 repetitions with knee extension at 70% of 1-repetition maximum. Lactate and root mean square (RMS) from the surface EMG of the vastus lateralis were calculated. RESULTS: Lactate increased in all protocols but was higher with BFR-I than with BFR-S and HL. RMS decreased under all conditions, with a larger effect size in BFR-I (1.47) than in BFR-S (0.66) and HL (0.59). DISCUSSION: BFR-I increases lactate, possibly as a result of reduced restoration of ATP. Muscle activation seems to be impacted by mechanical stress but may be reduced by metabolic stress. Muscle Nerve 57: 107-111, 2018.

Effects of resisted sprint training on sprinting ability and change of direction speed in professional soccer players.

Resisted sprint training consists of performing overloaded sprints, which may produce greater effects than traditional sprint training. We compared a resisted sprint training with overload control versus an unresisted sprint training program on performance in soccer players. Eighteen elite athletes were randomly assigned to resisted (RST) or unresisted sprint training protocol (UR). Before and after a 6-week training period, sprinting ability, change of direction speed (COD), vertical jumps (SJ and CMJ), mean power (MP) and mean propulsive power (MPP) at distinct loads were assessed. Both groups improved sprinting ability at all distances evaluated (5m: UR = 8%, RST = 7%; 10m: UR = 5%, RST = 5%; 15m: UR = 4%, RST = 4%; 20m: UR = 3%, RST = 3%; 25m: UR = 2%, RST = 3%;), COD (UR = 6%; RST = 6%), SJ (UR = 15%; RST = 13%) and CMJ (UR = 15%; RST = 15%). Additionally, both groups increased MP and MPP at all loads evaluated. The between-group magnitude-based inference analysis demonstrated comparable improvement ("trivial" effect) in all variables tested. Finally, our findings support the effectiveness of a short-term training program involving squat jump exercise plus sprinting exercises to improve the performance of soccer players.

Physiological Responses to and Athlete and Coach Perceptions of Exertion During Small-Sided Basketball Games.

Vaquera, A, Suárez-Iglesias, D, Guiu, X, Barroso, R, Thomas, G, and Renfree, A. Physiological responses to and athlete and coach perceptions of exertion during small-sided basketball games. J Strength Cond Res 32(10): 2949-2953, 2018-This study describes heart rate (HR) responses during different small-sided games (SSGs) in junior basketball players and identifies the level of agreement between athlete and coach perceptions of internal training load calculated using the in-task rating of perceived exertion (RPE) method. Over a 6-week period, 12 male junior basketball players, who played in the Spanish national under-18 League, played 7 games of one-a-side (1v1), 6 games of 2-a-side (2v2), 8 games of 5-a-side (5v5), and 5 games of superiority (3v2) situations. During 1v1, 2v2, 5v5, and 3v2, peak HRs were 90.27 ± 3.37%, 92.68 ± 3.29%, 92.01 ± 3.48%, and 88.74 ± 5.77% of HRmax, respectively. These differences were statistically significant between 1v1 and 2v2 (p < 0.01), 1v1 and 5v5 (p ≤ 0.05), 2v2 and 3v2 (p < 0.001), and 5v5 and 3v2 (p < 0.001). Mean HR was 79.5 ± 4.4%, 83.1 ± 4.2%, 91.2 ± 4.7%, and 78.5 ± 7.5% of HRmax during 1v1, 2v2, 5v5, and 3v2, respectively, and differences were observed between 1v1 and 2v2 (p < 0.001), 2v2 and 3v2 (p < 0.001), and 5v5 and 3v2 (p ≤ 0.05). There were differences in athletes and coaches in-task RPE in all SSGs (all p < 0.0001 apart from 5 × 5 p = 0.0019). The 2v2 format elicited a higher mean in-task RPE in comparison with all other SSGs (p < 0.001), possibly because 2v2 imposes a greater cognitive load.

Self-selected vs. Fixed Repetition Duration: Effects on Number of Repetitions and Muscle Activation in Resistance-Trained Men.

Nóbrega, SR, Barroso, R, Ugrinowitsch, C, da Costa, JLF, Alvarez, IF, Barcelos, C, and Libardi, CA. Self-selected vs. fixed repetition duration: effects on number of repetitions and muscle activation in resistance-trained men. J Strength Cond Res 32(9): 2419-2424, 2018-The aim of this study was to compare the effects of self-selected and fixed repetition duration (RD) on resistance exercise (RE) volume, muscle activation, and time under tension (TUT) per repetition and per session. Twelve resistance-trained men participated in the study. A randomized cross-over design was used and each participant performed 2 high-intensity RE protocols in a balanced order: (a) 3 sets of RE with self-selected RD (SELF); and (b) 3 sets of RE with fixed RD (2-second concentric and 2-second eccentric [FIX]). Muscle activation was assessed through surface electromyography (EMG) of the vastus lateralis and vastus medialis throughout RE sessions. Overall, RE volume was significantly greater for SELF (p = 0.01), whereas TUT per repetition was significantly greater for FIX (p = 0.0001). No significant differences between protocols were detected for TUT per session. Between-protocol comparisons revealed significantly greater EMG amplitude for SELF compared with FIX at S1 (p = 0.01), S2 (p = 0.03), and S3 (p = 0.03). Both SELF and FIX protocols produced significant increases in EMG amplitude from 25 to 100% (p < 0.001) of set completion. Between-protocol comparisons revealed significantly greater EMG amplitude for SELF compared with FIX at 75% (p = 0.03) and 100% (p = 0.01). In conclusion, self-selected RD resulted in greater volume and muscle activation compared with fixed RD in an RE session.

Effect of hand paddles and parachute on backstroke coordination and stroke parameters.

Hand paddles and parachutes have been used in order to overload swimmers, and consequently increase the propulsive force generation in swimming. However, their use may affect not only kinematical parameters (average speed, stroke length and stroke rate), but also time gaps between propulsive phases, assessed through the index of coordination (IdC). The objective of this study was to assess the effects of hand paddles and parachute use, isolated or combined, on kinematical parameters and coordination. Eleven swimmers (backstroke 50-m time: 29.16 ± 1.43 s) performed four 15-m trials in a randomised order at maximal intensity: (1) without implements (FREE), (2) with hand paddles (HPD), (3) with parachute (PCH) and (4) with hand paddles plus parachute (HPD+PCH). All trials were video-recorded (60 Hz) in order to assess average speed, stroke rate, stroke length, five stroke phases and index of coordination. When average swimming speed was compared to FREE, it was lower in PCH and HPD+PCH, and higher in HPD. Stroke rate decreased in all overloaded trials compared to FREE. The use of hand paddles and parachute increased and decreased stroke length, respectively. In addition, propulsive phase duration was increased when hand paddles were used, and time gaps shifted towards zero (no time gap), especially when hand paddles were combined with parachute. It is conceivable that the combined use of hand paddles and parachute, once allowing overloading both propulsive and resistive forces, provides a specific stimulus to improve muscle strength and propulsive continuity.

Effects of Different Combinations of Strength, Power, and Plyometric Training on the Physical Performance of Elite Young Soccer Players.

The combination of strength (ST) and plyometric training (PT) has been shown to be effective for improving sport-specific performance. However, there is no consensus about the most effective way to combine these methods in the same training session to produce greater improvements in neuromuscular performance of soccer players. Thus, the purpose of this study was to compare the effects of different combinations of ST and PT sequences on strength, jump, speed, and agility capacities of elite young soccer players. Twenty-seven soccer players (age: 18.9 ± 0.6 years) participated in an 8-week resistance training program and were divided into 3 groups: complex training (CP) (ST before PT), traditional training (TD) (PT before ST), and contrast training (CT) (ST and PT performed alternately, set by set). The experimental design took place during the competitive period of the season. The ST composed of half-squat exercises performed at 60-80% of 1 repetition maximum (1RM); the PT composed of drop jump exercises executed in a range from 30 to 45 cm. After the experimental period, the maximum dynamic strength (half-squat 1RM) and vertical jump ability (countermovement jump height) increased similarly and significantly in the CP, TD, and CT (48.6, 46.3, and 53% and 13, 14.2, and 14.7%, respectively). Importantly, whereas the TD group presented a significant decrease in sprinting speed in 10 (7%) and 20 m (6%), the other groups did not show this response. Furthermore, no significant alterations were observed in agility performance in any experimental group. In conclusion, in young soccer players, different combinations and sequences of ST and PT sets result in similar performance improvements in muscle strength and jump ability. However, it is suggested that the use of the CP and CT methods is more indicated to maintain/maximize the sprint performance of these athletes.

Effect of hand paddles and parachute on butterfly coordination.

This study investigated the effects of hand paddles, parachute and hand paddles plus parachute on the inter-limb coordination of butterfly swimming. Thirteen male swimmers were evaluated in four random maximal intensity conditions: without equipment, with hand paddles, with parachute and with hand paddles + parachute. Arm and leg stroke phases were identified by 2D video analysis to calculate the total time gap (T1: time between hands' entry in the water and high break-even point of the first undulation; T2: time between the beginning of the hand's backward movement and low break-even point of the first undulation; T3: time between the hand's arrival in a vertical plane to the shoulders and high break-even point of the second undulation; T4: time between the hand's release from the water and low break-even point of the second undulation). The swimming velocity was reduced and T1, T2 and T3 increased in parachute and hand paddles + parachute. No changes were observed in T4. Total time gap decreased in parachute and hand paddles + parachute. It is concluded that hand paddles do not influence the arm-to-leg coordination in butterfly, while parachute and hand paddles + parachute do change it, providing a greater propulsive continuity.

Effects of Strength Training Associated With Whole-Body Vibration Training on Running Economy and Vertical Stiffness.

Running economy (RE) is defined as the energy cost to maintain a submaximal running velocity and seems to be affected by individual's neuromuscular characteristics, such as stiffness level. Both resistance training (RT) and whole-body vibration training added to RT (WBV + RT) have been shown to influence those characteristics. Thus, it is conceivable that RT and WBV + RT could also affect RE. The objective of this study was to investigate if a 6-week training period of RT and WBV + RT influences RE and vertical stiffness (VS). Fifteen recreational runners were divided into RT or WBV + RT groups. Running economy, VS, and lower-limb maximum dynamic strength (1 repetition maximum [1RM] half-squat) were assessed before and after the 6-week training period. There was a main time effect for 1RM, but no other statistically significant difference was observed. Neither conventional RT nor RT performed on a WBV platform improved VS and RE in recreational long distance runners. It is possible that movement velocity was rather low, and utilization of stretch-shortening cycle might have been compromised, impairing any expected improvement in RE.

"Falling Behind," "Letting Go," and Being "Outsprinted" as Distinct Features of Pacing in Distance Running.

INTRODUCTION: In distance running, pacing is characterized by changes in speed, leading to runners dropping off the leader's pace until a few remain to contest victory with a final sprint. Pacing behavior has been well studied over the last 30 years, but much remains unknown. It might be related to finishing position, finishing time, and dependent on critical speed (CS), a surrogate of physiologic capacity. We hypothesized a relationship between CS and the distance at which runners "fell behind" and "let go" from the leader or were "outsprinted" as contributors to performance. METHODS: 100-m split times were obtained for athletes in the men's 10,000-m at the 2008 Olympics (N = 35). Split times were individually compared with the winner at the point of "falling behind" (successive split times progressively slower than the winner), "letting go" (large increase in time for distance compared with winner), or "outsprinted" (falling behind despite active acceleration) despite being with the leader with 400 m remaining. RESULTS: Race times ranged between 26:55 and 29:23 (world record = 26:17). There were 3 groups who fell behind at ∼1000 (n = 11), ∼6000 (n = 16), and ∼9000 m (n = 2); let go at ∼4000 (n = 10), ∼7000 (n = 14), and ∼9500 m (n = 5); or were outkicked (n = 6). There was a moderate correlation between CS and finishing position (r = .82), individual mean pace (r = .79), "fell behind" distance (r = .77), and "let go" distance (r = .79). D' balance was correlated with performance in the last 400 m (r = .87). CONCLUSIONS: Athletes displayed distinct patterns of falling behind and letting go. CS serves as a moderate predictor of performance and final placing. Final placing during the sprint is related to preservation of D' balance.

Evolution of 1500-m Olympic Running Performance.

PURPOSE: This study determined the evolution of performance and pacing for each winner of the men's Olympic 1500-m running track final from 1924 to 2020. METHODS: Data were obtained from publicly available sources. When official splits were unavailable, times from sources such as YouTube were included and interpolated from video records. Final times, lap splits, and position in the peloton were included. The data are presented relative to 0 to 400 m, 400 to 800 m, 800 to 1200 m, and 1200 to 1500 m. Critical speed and D' were calculated using athletes' season's best times. RESULTS: Performance improved ∼25 seconds from 1924 to 2020, with most improvement (∼19 s) occurring in the first 10 finals. However, only 2 performances were world records, and only one runner won the event twice. Pacing evolved from a fast start-slow middle-fast finish pattern (reverse J-shaped) to a slower start with steady acceleration in the second half (J-shaped). The coefficient of variation for lap speeds ranged from 1.4% to 15.3%, consistent with a highly tactical pacing pattern. With few exceptions, the eventual winners were near the front throughout, although rarely in the leading position. There is evidence of a general increase in both critical speed and D' that parallels performance. CONCLUSIONS: An evolution in the pacing pattern occurred across several "eras" in the history of Olympic 1500-m racing, consistent with better trained athletes and improved technology. There has been a consistent tactical approach of following opponents until the latter stages, and athletes should develop tactical flexibility, related to their critical speed and D', in planning prerace strategy.

The effects of different intensities and durations of the general warm-up on leg press 1RM.

The precision of maximum strength assessments (1 repetition maximum; 1RM) is important to evaluate the functional capacity and to prescribe and monitor the training load. Several factors can affect the precision of 1RM tests, including the warm-up procedure. General and specific warm-up routines are recommended to enhance performance. The effects of a specific warm-up have already been acknowledged in improving performance. However, the effects of a general warm-up (GWU) are unclear but seem to depend on its ability to increase muscle temperature while avoiding fatigue. Furthermore, temperature elevation is dependent on both the duration and the intensity of the activity, which may eventually affect 1RM performance. The objective of this study was to investigate the effect of different intensities and durations of GWU on 1RM performance. Sixteen strength-trained men were tested for 1RM leg press after 4 GWU conditions after specific warm-up: short duration and low intensity (SDLI; i.e., 5 minutes at 40% V[Combining Dot Above]O2max), long duration and low intensity (LDLI; i.e., 15 minutes at 40% V[Combining Dot Above]O2max), short duration and moderate intensity (SDMI; i.e., 5 minutes at 70% V[Combining Dot Above]O2max), long duration and moderate intensity (LDMI; i.e., 15 minutes at 70% V[Combining Dot Above]O2max), and the control (CTRL) no-GWU condition. Leg press 1RM values were higher (on average 3%) when subjects performed LDLI (367.8 ± 70.1 kg; p = 0.01), compared with the other 4 conditions. After the LDMI condition, 1RM values were lower (on average -4%) than in the other 4 conditions (345.6 ± 70.5 kg; p = 0.01). There were no differences between SDMI, SDLI, and CTRL (359.4 ± 69.2 kg, 359.1 ± 69.3 kg, and 359.4 ± 70.4 kg, respectively; p = 0.99). According to our results, long-duration low-intensity general warm-up seems be appropriately to improve 1RM performance in strength-trained individuals.

Serum Metabolites Associated with Muscle Hypertrophy after 8 Weeks of High- and Low-Load Resistance Training.

The mechanisms responsible for the similar muscle growth attained with high- and low-load resistance training (RT) have not yet been fully elucidated. One mechanism is related to the mechanical stimulus and the level of motor unit recruitment; another mechanism is related to the metabolic response. We investigated the electromyographic signal amplitude (sEMG) and the general metabolic response to high-load RT (HL) and low-load resistance training (LL). We measured muscle thickness by ultrasound, sEMG amplitude by electromyography, and analysis of metabolites expressed through metabolomics. No differences were observed between the HL and LL groups for metabolic response and muscle thickness. A greater amplitude of sEMG was observed in the HL group. In addition, a correlation was observed between changes in muscle thickness of the vastus lateralis muscle in the HL group and levels of the metabolites carnitine, creatine, 3-hydroxyisovalerate, phenylalanine, asparagine, creatine phosphate, and methionine. In the LL group, a correlation was observed between changes in muscle thickness of the vastus lateralis muscle and levels of the metabolites acetoacetate, creatine phosphate, and oxypurinol. These correlations seem to be related to the characteristics of activated muscle fibers, the metabolic demand of the training protocols used, and the process of protein synthesis.