Fatigue and Recovery Profiles of Unilateral Resistance Exercise in a Resistance Trained Population

Recent data shows that fatiguing unilateral isometric contractions affect the performance of the non-exercising, contralateral muscles (i.e., cross-over effect). However, there is limited data on the time-course of the contralateral response, whether the effects occur during resistance exercise, and the influence of resistance training experience. PURPOSE: To examine force and electromyographic (EMG) activity during and after a fatiguing unilateral resistance exercise protocol for the ipsilateral and contralateral elbow flexors in a resistance trained population. METHODS: Eight participants (7 right hand dominant; mean age=22yrs; 7 males; resistance trained with ≥ 2days/week upper body) visited the laboratory on two days separated by ≥ 48 hrs. On the first visit, maximal dynamic strength was determined for the ipsilateral arm and control procedures for maximal isometric strength of the contralateral arm was performed. On the second visit, participants completed 4 sets of unilateral dynamic bicep curls to failure with 50% 1RM with 2 min rest intervals between sets. Maximal voluntary contractions (MVC) and EMG activity of the elbow flexors were recorded immediately before exercise and after each set for both arms, except for set 1 and 3 where only the ipsilateral arm performed MVC’s. The responses during acute recovery were recorded at 2.5 min, 5 mins, and 10 mins post exercise. Separate repeated measures ANOVA tests were performed on the MVC and EMG responses for each arm. Alpha was set at 0.05. RESULTS: The results of the analysis show that for the ipsilateral arm, baseline MVC values declined to set 1 (p\u3c0.01; ~26%), with no significant differences in force loss thereafter for set 2 (~29%), set 3 (~28%), set 4 (~30%), recovery 1 (~28%), recovery 2 (~27%), or recovery 3 (~24%). There was no significant change in maximal EMG activity for the ipsilateral biceps brachii (p=0.189; ηp2 =0.177). For the contralateral biceps brachii, there was no significant difference across time in maximal EMG activity between the fatigue visit versus the control visit (p=0.732; ηp2=0.018). However, collapsed across visit, there was a significant decrease in maximal EMG amplitude (p\u3c0.01; ηp2=0.614) that appears to be explained by the fatigue visit (p=0.319; d=0.379). For the contralateral arm, there was no significant change in MVC across time for either visit (p=0.166; ηp2=0.211). CONCLUSION: These results show that following acute resistance exercise performed to failure, there is no change in maximal force of the contralateral elbow flexors. This finding brings into question whether the cross-over effect of fatigue occurs during resistance exercise or in resistance trained populations. The fatigability profile of the ipsilateral arm demonstrates there was no compounding effect on force loss with additional sets to failure. The lack of force recovery following acute resistance exercise emphasizes the importance of task dependency. The applications of these data suggests that relative fatigability may not be a useful metric to monitor training session outcomes

Influence of Scanning Plane and Echo Intensity Correction on Relationships Between Muscle Size and Fitness

B-mode ultrasonography is an accessible and reliable tool to measure muscle size and echogenicity. Measures of muscle thickness (MT), muscle cross-sectional area (mCSA), and echo intensity (EI) are commonly acquired in the sagittal or transverse planes, and with the extended field of view technique. However, whether these outcomes show unique relationships with muscle fitness across the scanning planes is unknown. PURPOSE: To identify the relationships between measurements of skeletal muscle size and echo intensity with muscle strength and local muscle endurance in a habitually resistance-trained population. METHODS: Twenty resistance-trained participants (Females: n = 10; Males: n = 10) underwent ultrasonography imaging in the sagittal and transverse planes and with the extended field of view technique. The participant\u27s maximal dynamic strength (1RM bicep curl) and local muscle endurance (4x failure @ 50%1RM) were measured on separate days. The ultrasound-derived measures of MT, mCSA, EI, and adipose tissue thickness corrected echo intensity (cEI) in each scanning plane were examined for their associations with 1RM strength and total repetitions across the four sets with stepwise multiple linear regression. RESULTS: The analyses show the best predictor of 1RM strength and local muscle endurance was sagittal MT (adj. R2 = 0.682) and sagittal cEI (adj. R2 = 0.449), respectively. A positive relationship was demonstrated between strength and transverse MT (R2 = 0.661) and the extended field of view mCSA (R2 = 0.643). A negative relationship was shown between local muscle endurance and cEI in the transverse plane (R2 = 0.265) and the extended field of view scan (R2 = 0.309). However, no associations were shown with uncorrected EI. CONCLUSIONS: Overall, for the biceps brachii, sagittal plane imaging shows the strongest relationships with muscle fitness. While each scanning plane supports the muscle size – strength and echogenicity – endurance relationships, imaging in the sagittal plane is sufficient for time-restricted scenarios that are common in laboratory and allied health settings. These findings suggest that correcting EI for adipose tissue thickness should be done when inferences are being made regarding EI as an indicator of muscle quality

Applications of the Critical Power Model to Dynamic Constant External Resistance Exercise: A Brief Review of the Critical Load Test

The study and application of the critical power (CP) concept has spanned many decades. The CP test provides estimates of two distinct parameters, CP and W0 , that describe aerobic and anaerobic metabolic capacities, respectively. Various mathematical models have been used to estimate the CP and W0 parameters across exercise modalities. Recently, the CP model has been applied to dynamic constant external resistance (DCER) exercises. The same hyperbolic relationship that has been established across various continuous, whole-body, dynamic movements has also been demonstrated for upper-, lower-, and whole-body DCER exercises. The asymptote of the load versus repetition relationship is defined as the critical load (CL) and the curvature constant is L0 . The CL and L0 can be estimated from the same linear and non-linear mathematical models used to derive the CP. The aims of this review are to (1) provide an overview of the CP concept across continuous, dynamic exercise modalities; (2) describe the recent applications of the model to DCER exercise; (3) demonstrate how the mathematical modeling of DCER exercise can be applied to further our understanding of fatigue and individual performance capabilities; and (4) make initial recommendations regarding the methodology for estimating the parameters of the CL test

Muscular Performance and Neuromuscular Fatigue are not Sex-Dependent During Low-Load Fatiguing Bilateral Leg Extension Exercise

Purpose. This study examined the sex-related differences in muscular performance and neuromuscular (electromyographic [EMG] and mechanomyographic [MMG] amplitude [AMP] and mean power frequency [MPF]) responses during fatiguing leg extension repetitions performed at the critical load (CL). Methods. Eleven men and nine women completed one-repetition maximum (1RM) testing, repetitions to failure at 50, 60, 70, and 80% 1RM to determine CL, and repetitions to failure at CL, on separate days. The EMG and MMG, AMP and MPF signals and number of repetitions completed were recorded. Results. There were no sex-dependent responses in the %1RM that corresponded to, the number of repetitions completed at, or the neuromuscular responses during repetitions performed to failure at CL. There were time-dependent responses in EMG AMP from 25-100% of total repetitions completed, respectively. The EMG MPF and MMG MPF demonstrated fatigue-induced decreases from 50-100% and at 100% of total repetitions completed, respectively. There was no change over time for MMG AMP. Conclusions. These findings indicated men and women responded similarly to leg extension exercise performed at the CL. Further, sex-dependent responses to fatiguing exercise may be related to the amount of active muscle mass engaged in exercise and the corresponding afferent feedback that influences peripheral fatigue and central drive during fatiguing tasks

Unilateral Handgrip Holds to Failure Result in Sex-Dependent Contralateral Facilitation

There can be differences in fatigue characteristics between men and women. In some cases, these differences may be manifested in unique strength responses in the fatigued and non-fatigued limbs following a unilateral fatiguing task. PURPOSE: This study examined changes in maximal voluntary isometric contraction (MVIC) force following dominant (Dm) and nondominant (NDm) unilateral, isometric handgrip holds to failure (HTF) for the exercised ipsilateral (IPS) and non-exercised contralateral (CT) limbs. Sex- and hand- (Dm vs NDm) dependent responses in HTF time, performance fatiguability (PF, %D in MVIC) for the exercised IPS limb, as well as changes in MVIC force for the CT limb following the HTF were examined. METHODS: Ten men and 10 women (Age = 22.2 yrs) performed an isometric, HTF at 50% MVIC for the Dm and NDm hand on separate days. Prior to, and immediately after the HTF, a MVIC was performed on the IPS and CT limbs, in a randomized order. A 2 (hand [Dm, NDm]) x 2 (limb [IPS, CON]) x 2 (time [pre-HTF, post-HTF]) x 2 (sex [men, women]) mixed-model ANOVA was used to examine the MVIC force (kg) and a 2 (hand [Dm, NDm]) x 2 (sex [men, women]) mixed-model ANOVA was used to examine time for the HTF. RESULTS: The Dm (130.3 ± 36.8s) HTF (collapsed across sex) was significantly longer (p = 0.002) than the NDm (112.1 ± 34.3s). The men (collapsed across hand) demonstrated IPS (%Δ= 22.9 ± 10.8%) PF and CT facilitation (%Δ= -6.1 ±6.9%) following the HTF, while the women demonstrated differences in PF between the Dm and NDm hands for the IPS (%Δ Dm = 28.0 ± 9.4%; NDm = 32.3% ± 10.1%; p = 0.027), but not the CT limb (%Δ Dm= -1.6 ± 5.7%; NDm = 1.7 ± 5.9%). CONCLUSIONS: Despite the greater fatigue resistance for the Dm compared to the NDm hand, there were no differences in PF for the IPS side for the men, but lesser IPS PF for Dm compared to NDm hand for the women. The cross-over facilitation of the CT limb for men, but not women, following a unilateral, isometric handgrip HTF may be related to post-activation potentiation

The Influence of Sonographer Experience on Skeletal Muscle Image Acquisition and Analysis

The amount of experience with ultrasonography may influence measurement outcomes while images are acquired or analyzed. The purpose of this study was to identify the interrater reliability of ultrasound image acquisition and image analysis between experienced and novice sonographers and image analysts, respectively. Following a brief hands-on training session (2 h), the experienced and novice sonographers and analysts independently performed image acquisition and analyses on the biceps brachii, vastus lateralis, and medial gastrocnemius in a sample of healthy participants (n = 17). Test–retest reliability statistics were computed for muscle thickness (transverse and sagittal planes), muscle cross-sectional area, echo intensity and subcutaneous adipose tissue thickness. The results show that image analysis experience generally has a greater impact on measurement outcomes than image acquisition experience. Interrater reliability for measurements of muscle size during image acquisition was generally good–excellent (ICC2,1: 0.82–0.98), but poor–moderate for echo intensity (ICC2,1: 0.43–0.77). For image analyses, interrater reliability for measurements of muscle size for the vastus lateralis and biceps brachii was poor–moderate (ICC2,1: 0.48–0.70), but excellent for echo intensity (ICC2,1: 0.90–0.98). Our findings have important implications for laboratories and clinics where members possess varying levels of ultrasound experience

Applications of the Critical Power Model to Dynamic Constant External Resistance Exercise: A Brief Review of the Critical Load Test

The study and application of the critical power (CP) concept has spanned many decades. The CP test provides estimates of two distinct parameters, CP and W′, that describe aerobic and anaerobic metabolic capacities, respectively. Various mathematical models have been used to estimate the CP and W′ parameters across exercise modalities. Recently, the CP model has been applied to dynamic constant external resistance (DCER) exercises. The same hyperbolic relationship that has been established across various continuous, whole-body, dynamic movements has also been demonstrated for upper-, lower-, and whole-body DCER exercises. The asymptote of the load versus repetition relationship is defined as the critical load (CL) and the curvature constant is L′. The CL and L′ can be estimated from the same linear and non-linear mathematical models used to derive the CP. The aims of this review are to (1) provide an overview of the CP concept across continuous, dynamic exercise modalities; (2) describe the recent applications of the model to DCER exercise; (3) demonstrate how the mathematical modeling of DCER exercise can be applied to further our understanding of fatigue and individual performance capabilities; and (4) make initial recommendations regarding the methodology for estimating the parameters of the CL test

Unilateral Handgrip Holds to Failure Result in Sex-Dependent Contralateral Facilitation

International Journal of Exercise Science 15(4): 782-796, 2022. This study examined changes in maximal voluntary isometric contraction (MVIC) force following dominant (Dm) and nondominant (NDm) unilateral, handgrip isometric holds to failure (HTF) for the exercised ipsilateral (IPS) and non-exercised contralateral (CON) limbs and determined if there are sex- and hand- (Dm vs NDm) dependent responses in the HTF time, performance fatigability (PF) for the exercised IPS limb, and changes in MVIC force for the CON limb after unilateral fatigue. Ten men and 10 women (Age = 22.2 years) completed an isometric HTF at 50% MVIC for the Dm and NDm hand on separate days. Prior to, and immediately after the HTF, an MVIC was performed on the IPS and CON limbs, in a randomized order. The Dm (130.3 ± 36.8 s) HTF (collapsed across sex) was significantly longer (p = 0.002) than the NDm (112.1 ± 34.3 s). The men (collapsed across hand) demonstrated IPS (%D = 22.9 ± 10.8%) PF and CON facilitation (%D = -6.1 ± 6.9%) following the HTF, while the women demonstrated differences in PF between the Dm and NDm hands for the IPS (%D Dm = 28.0 ± 9.4%; NDm = 32.3% ± 10.1%; p = 0.027), but not the CON limb (%D Dm = -1.6 ± 5.7%; NDm = 1.7 ± 5.9%). The cross-over facilitation of the CON limb for men, but not women, following a unilateral, isometric handgrip HTF may be related to post-activation potentiation

Unilateral Handgrip Holds to Failure Result in Sex-Dependent Contralateral Facilitation

There can be differences in fatigue characteristics between men and women. In some cases, these differences may be manifested in unique strength responses in the fatigued and non-fatigued limbs following a unilateral fatiguing task. PURPOSE: This study examined changes in maximal voluntary isometric contraction (MVIC) force following dominant (Dm) and nondominant (NDm) unilateral, isometric handgrip holds to failure (HTF) for the exercised ipsilateral (IPS) and non-exercised contralateral (CT) limbs. Sex- and hand- (Dm vs NDm) dependent responses in HTF time, performance fatiguability (PF, %D in MVIC) for the exercised IPS limb, as well as changes in MVIC force for the CT limb following the HTF were examined. METHODS: Ten men and 10 women (Age = 22.2 yrs) performed an isometric, HTF at 50% MVIC for the Dm and NDm hand on separate days. Prior to, and immediately after the HTF, a MVIC was performed on the IPS and CT limbs, in a randomized order. A 2 (hand [Dm, NDm]) x 2 (limb [IPS, CON]) x 2 (time [pre-HTF, post-HTF]) x 2 (sex [men, women]) mixed-model ANOVA was used to examine the MVIC force (kg) and a 2 (hand [Dm, NDm]) x 2 (sex [men, women]) mixed-model ANOVA was used to examine time for the HTF. RESULTS: The Dm (130.3 ± 36.8s) HTF (collapsed across sex) was significantly longer (p = 0.002) than the NDm (112.1 ± 34.3s). The men (collapsed across hand) demonstrated IPS (%Δ= 22.9 ± 10.8%) PF and CT facilitation (%Δ= -6.1 ±6.9%) following the HTF, while the women demonstrated differences in PF between the Dm and NDm hands for the IPS (%Δ Dm = 28.0 ± 9.4%; NDm = 32.3% ± 10.1%; p = 0.027), but not the CT limb (%Δ Dm= -1.6 ± 5.7%; NDm = 1.7 ± 5.9%). CONCLUSIONS: Despite the greater fatigue resistance for the Dm compared to the NDm hand, there were no differences in PF for the IPS side for the men, but lesser IPS PF for Dm compared to NDm hand for the women. The cross-over facilitation of the CT limb for men, but not women, following a unilateral, isometric handgrip HTF may be related to post-activation potentiation

The Influence of Sonographer Experience on Skeletal Muscle Image Acquisition and Analysis

The amount of experience with ultrasonography may influence measurement outcomes while images are acquired or analyzed. The purpose of this study was to identify the interrater reliability of ultrasound image acquisition and image analysis between experienced and novice sonographers and image analysts, respectively. Following a brief hands-on training session (2 h), the experienced and novice sonographers and analysts independently performed image acquisition and analyses on the biceps brachii, vastus lateralis, and medial gastrocnemius in a sample of healthy participants (n = 17). Test–retest reliability statistics were computed for muscle thickness (transverse and sagittal planes), muscle cross-sectional area, echo intensity and subcutaneous adipose tissue thickness. The results show that image analysis experience generally has a greater impact on measurement outcomes than image acquisition experience. Interrater reliability for measurements of muscle size during image acquisition was generally good–excellent (ICC2,1: 0.82–0.98), but poor–moderate for echo intensity (ICC2,1: 0.43–0.77). For image analyses, interrater reliability for measurements of muscle size for the vastus lateralis and biceps brachii was poor–moderate (ICC2,1: 0.48–0.70), but excellent for echo intensity (ICC2,1: 0.90–0.98). Our findings have important implications for laboratories and clinics where members possess varying levels of ultrasound experience