Trained females exhibit less fatigability than trained males after a heavy knee extensor resistance exercise session

Differences in knee flexor and extensor force and kinematic variables in rural versus urban area female students in Romania

The study aimed to identify and explain the typical differences in low-intensity high-volume resistance training (LIHV-RT) performances for major muscle groups between rural versus urban young female students to establish the relevant set of quantitative and qualitative resistance training parameters. The study sample included 46 recreational active female students at the Transilvania University of Brașov, (mean ± SD age, 20 ± 1 year; body mass, 60 ± 3 kg; height, 160 ± 4 cm) grouped urban vs. rural. The study used modified resistance exercise machines for the hamstring- and quadricep-group muscles, equipped with a dynamometer and sensors for identifying developed forces and accelerations. A number of 368 tests were performed, representing two attempts for each subject, for knee flexion and knee extension exercises, with two different loads. For the performance analysis some variables were considered: the maximum number of repetition until failure, maximum force developed, maximum acceleration, the duration of the set and the mean time per repetition. The maximum number of repetition to failure shows a significant higher value for rural than urban in case of knee flexion (d = 0.98 [0.32, 1.54] for load 1(L1) and d = 0.65 [0.03, 1.21] for load 2(L2)) and in case of knee extension (d = 1.89 [1.11, 2.48] for L1 and d = 1.67 [0.92, 2.25] for L2). The total duration of the sets shows a significant higher value for rural than urban in case of knee flexion (d = 0.84 [0.19, 1.39] for L2) and in case of knee extension (d = 1.46 [0.74, 2.03] for L1 and d = 1.56 [0.98, 2.14] for L2). Additionally we found differences in the quality of the relevant repetitions execution and in the impulse developed during the LIHV- MNRF sets. The study's main finding was that there are differences in LIHV-RT performances knee flexion and knee extension antagonistic exercises, between rural and urban female students. We concluded that the obtained results allow teachers to understand the optimal design of RT programs for the different groups of participants, in order to adapt their teaching techniques so that their final objectives are achieved, insisting on particular aspects of the theoretical or practical contents.

Narrative Review of Sex Differences in Muscle Strength, Endurance, Activation, Size, Fiber Type, and Strength Training Participation Rates, Preferences, Motivations, Injuries, and Neuromuscular Adaptations

ABSTRACT

Nuzzo, JL. Narrative review of sex differences in muscle strength, endurance, activation, size, fiber type, and strength training participation rates, preferences, motivations, injuries, and neuromuscular adaptations. J Strength Cond Res 37(2): 494-536, 2023-Biological sex and its relation with exercise participation and sports performance continue to be discussed. Here, the purpose was to inform such discussions by summarizing the literature on sex differences in numerous strength training-related variables and outcomes-muscle strength and endurance, muscle mass and size, muscle fiber type, muscle twitch forces, and voluntary activation; strength training participation rates, motivations, preferences, and practices; and injuries and changes in muscle size and strength with strength training. Male subjects become notably stronger than female subjects around age 15 years. In adults, sex differences in strength are more pronounced in upper-body than lower-body muscles and in concentric than eccentric contractions. Greater male than female strength is not because of higher voluntary activation but to greater muscle mass and type II fiber areas. Men participate in strength training more frequently than women. Men are motivated more by challenge, competition, social recognition, and a desire to increase muscle size and strength. Men also have greater preference for competitive, high-intensity, and upper-body exercise. Women are motivated more by improved attractiveness, muscle "toning," and body mass management. Women have greater preference for supervised and lower-body exercise. Intrasexual competition, mate selection, and the drive for muscularity are likely fundamental causes of exercise behaviors in men and women. Men and women increase muscle size and strength after weeks of strength training, but women experience greater relative strength improvements depending on age and muscle group. Men exhibit higher strength training injury rates. No sex difference exists in strength loss and muscle soreness after muscle-damaging exercise.

Mouth rinsing and ingesting salty or bitter solutions does not influence corticomotor excitability or neuromuscular function

PURPOSE

To explore the effect of tasting unpleasant salty or bitter solutions on lower limb corticomotor excitability and neuromuscular function.

METHODS

Nine females and eleven males participated (age: 27 ± 7 years, BMI: 25.3 ± 4.0 kg m^-2). Unpleasant salty (1 M) and bitter (2 mM quinine) solutions were compared to water, sweetened water, and no solution, which functioned as control conditions. In a non-blinded randomized cross-over order, each solution was mouth rinsed (10 s) and ingested before perceptual responses, instantaneous heart rate (a marker of autonomic nervous system activation), quadricep corticomotor excitability (motor-evoked potential amplitude) and neuromuscular function during a maximal voluntary contraction (maximum voluntary force, resting twitch force, voluntary activation, 0-50 ms impulse, 0-100 impulse, 100-200 ms impulse) were measured.

RESULTS

Hedonic value (water: 47 ± 8%, sweet: 23 ± 17%, salt: 71 ± 8%, bitter: 80 ± 10%), taste intensity, unpleasantness and increases in heart rate (no solution: 14 ± 5 bpm, water: 18 ± 5 bpm, sweet: 20 ± 5 bpm, salt: 24 ± 7 bpm, bitter: 23 ± 6 bpm) were significantly higher in the salty and bitter conditions compared to control conditions. Nausea was low in all conditions (< 15%) but was significantly higher in salty and bitter conditions compared to water (water: 3 ± 5%, sweet: 6 ± 13%, salt: 7 ± 9%, bitter: 14 ± 16%). There was no significant difference between conditions in neuromuscular function or corticomotor excitability variables.

CONCLUSION

At rest, unpleasant tastes appear to have no influence on quadricep corticomotor excitability or neuromuscular function. These data question the mechanisms via which unpleasant tastes are proposed to influence exercise performance.

Functional Impact of Post-exercise Cooling and Heating on Recovery and Training Adaptations: Application to Resistance, Endurance, and Sprint Exercise

The application of post-exercise cooling (e.g., cold water immersion) and post-exercise heating has become a popular intervention which is assumed to increase functional recovery and may improve chronic training adaptations. However, the effectiveness of such post-exercise temperature manipulations remains uncertain. The aim of this comprehensive review was to analyze the effects of post-exercise cooling and post-exercise heating on neuromuscular function (maximal strength and power), fatigue resistance, exercise performance, and training adaptations. We focused on three exercise types (resistance, endurance and sprint exercises) and included studies investigating (1) the early recovery phase, (2) the late recovery phase, and (3) repeated application of the treatment. We identified that the primary benefit of cooling was in the early recovery phase (< 1 h post-exercise) in improving fatigue resistance in hot ambient conditions following endurance exercise and possibly enhancing the recovery of maximal strength following resistance exercise. The primary negative impact of cooling was with chronic exposure which impaired strength adaptations and decreased fatigue resistance following resistance training intervention (12 weeks and 4–12 weeks, respectively). In the early recovery phase, cooling could also impair sprint performance following sprint exercise and could possibly reduce neuromuscular function immediately after endurance exercise. Generally, no benefits of acute cooling were observed during the 24–72-h recovery period following resistance and endurance exercises, while it could have some benefits on the recovery of neuromuscular function during the 24–48-h recovery period following sprint exercise. Most studies indicated that chronic cooling does not affect endurance training adaptations following 4–6 week training intervention. We identified limited data employing heating as a recovery intervention, but some indications suggest promise in its application to endurance and sprint exercise.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

Fatigability of the knee extensors following high- and low-load resistance exercise sessions in trained men

PURPOSE

Fatigability after gym-based resistance exercises with high and low loads has not been well described, thus limiting the translation of exhaustive low-weight prescription into athletic practice. We compared the fatigability and recovery of the knee extensor muscles for up to 1H after sessions that involved either high- or low-load resistance exercises.

METHODS

16 trained men performed two resistance exercise sessions between 5 and 7 days apart. The LIGHT session involved five sets to task failure at 50% of maximal knee-extension strength, whereas the HEAVY session accrued repetitions across seven sets at intensities ≥ 80% maximal knee-extension strength. Measures of quadriceps maximal torque and rate of torque development were measured before, after, and 1H after each exercise session. Muscle activation (electromyography and voluntary activation) and contractility were measured from doublet stimulation of the femoral nerve during and after maximal contractions, respectively.

RESULTS

Greater declines in maximal rate of torque development were observed after the LIGHT compared with the HEAVY session (p < 0.001), with full recovery after 1H. Voluntary activation (100-Hz doublet stimulation) and surface electromyograms were reduced immediately after the HEAVY session only (p < 0.05), with greater declines in quadriceps twitch amplitudes after the LIGHT session (p < 0.01). Voluntary activation (100-Hz doublet stimulation) was reduced at 1H after both the HEAVY and LIGHT sessions (p < 0.05).

CONCLUSIONS

Despite differences in the decreases in muscle activation and contractility after high- and low-load resistance-exercise sessions, recovery of neuromuscular function was essentially complete after 1H of rest for both sessions.

Acute Neuromuscular Response to Team Sports-specific Running, Resistance, and Concurrent Training: A Cross-over Study

PURPOSE

To examine the changes in muscle contractile function, voluntary activation, and muscle damage following lower limb resistance training (RT), intermittent sprint exercise and concurrent training (CT).

METHODS

Ten male, recreational team sport athletes with a history of RT participated in a randomised cross-over study involving an intermittent sprint protocol (ISP), lower limb RT and CT (ISP and RT separated by 1 h). Prior to (PRE), immediately post (POST), 24 h and 48 h following each exercise condition, quadriceps muscle activation, voluntary activation, muscle contractile function (evoked twitch responses), creatine kinase (CK), muscle soreness and POMS-fatigue were recorded.

RESULTS

Quadriceps contractile function was hampered in all conditions, with a significantly greater decline observed POST RT (58.4 ± 18.0%) and CT (54.8 ± 8.6%) compared to ISP (35.9 ± 10.7%; p < 0.05), recovering at 48 h following all exercise conditions. POMS-fatigue ratings increased at POST in all conditions with CT and ISP eliciting the greatest increase, returning to baseline 48 h following all exercise conditions. Quadriceps muscle soreness remained elevated from PRE at 48 h following all exercise conditions. No changes across time were observed for voluntary activation and quadriceps surface EMG amplitude following any exercise condition. The volume and load lifted in the RT session was unaffected by prior intermittent exercise (ISP) in CT.

CONCLUSION

RT impairs contractile function which is not exacerbated when performed 1 h following the ISP. Contractile function following all exercise conditions displayed the same recovery profile (48 h) despite the post-exercise decrement being smaller following the ISP compared to RT and CT. Prior intermittent sprint exercise does not negatively impact the volume of exercise performed in a lower limb RT session.

Declines in muscle contractility and activation during isometric contractions of the knee extensors vary with contraction intensity and exercise volume

NEW FINDINGS

What is the central question of this study? Is there a critical threshold beyond which the loss of muscle contractility is regulated by the level of muscle activation during single-limb exercise of differing intensities and volumes? What is the main finding and its importance? Plateaus in the decline in muscle contractility during single-limb knee extension depended on both exercise volume and contraction intensity.  A plateau was only evident with an increase in exercise volume.  Muscle activation increased and did not decline despite substantial reductions in contractility. The findings indicate that the decrease in muscle contractility exhibited by resistance-trained men during the performance of submaximal isometric contractions with the knee extensors was not regulated by the level of muscle activation.

ABSTRACT

Our study examined the influence of contraction intensity and exercise volume on changes in muscle contractility and activation of the knee extensor muscles. Maximal voluntary torque (MVT) and rate of change in torque, surface electromyograms, voluntary activation, V-waves and quadriceps resting twitch measures were assessed in 10 resistance-trained men during two experimental sessions. Each session began with an initial baseline series of contractions at a fixed intensity of 40% or 80% MVT. The 40%-only session continued with five contractions to task failure at 40% MVT. The 80% session continued with five contractions to failure each at 80%, 60% and 40% MVT. Greater reductions in MVT were observed during the baseline contractions of the 40%-only session compared with the 80% session at each matched-volume time point (P < 0.05), with similar changes in twitch values (P < 0.001). MVT and twitch values plateaued at each intensity during the 80% session and were significantly different across intensities: 80% > 60% > 40% (P < 0.001). There were no differences for measures during the five contractions at 40% MVT performed on the different days, despite a greater volume of exercise performed prior to the 40% MVT during the 80% session. At each contraction intensity, a plateau in contractility loss was observed as more contractions were performed. We found that initial increases in muscle activation were maintained in the presence of increases in exercise volume and, in contrast to the critical-threshold hypothesis, did not decline in parallel with reductions in muscle contractility.

Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (−19%) was comparable to late RFD (−19%) but lower compared to both peak RFD (−25%) and early RFD (−23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD.

Sex Differences in Adaptations in Muscle Strength and Size Following Resistance Training in Older Adults: A Systematic Review and Meta-analysis

BACKGROUND

Reductions in muscle size and strength occur with aging. These changes can be mitigated by participation in resistance training. At present, it is unknown if sex contributes to differences in adaptation to resistance training in older adults.

OBJECTIVE

The aim of this systematic review was to determine if sex differences are apparent in adaptations to resistance training in older adults.

DESIGN

Systematic review with meta-analysis.

DATA SOURCES

Web of Science; Science Direct; SPORTDiscus; CINAHL; and MEDLINE were searched from inception to June 2020.

ELIGIBILITY CRITERIA

Studies where males and females older than 50 years of age performed identical resistance training interventions and had outcome measures of muscle strength or size.

RESULTS

We initially screened 5337 studies. 30 studies (with 41 comparison groups) were included in our review (1410 participants; 651 males, 759 females). Mean study quality was 14.7/29 on a modified Downs and Black checklist, considered moderate quality. Females gained more relative lower-body strength than males (g = - 0.21 [95% CI - 0.33, - 0.10], p = 0.0003) but there were no differences in relative change for upper-body strength (g = - 0.29 [95% CI - 0.62, 0.04], p = 0.08) or relative muscle size (g = 0.10 [95% CI - 0.04, 0.23], p = 0.16). Males gained more absolute upper-body strength (g = 0.48 [95% CI 0.09, 0.88], p = 0.016), absolute lower-body strength (g = 0.33 [95% CI 0.19, 0.47], p < 0.0001), and absolute muscle size (g = 0.45 [95% CI 0.23, 0.66], p < 0.0001).

CONCLUSION

Our results indicate that sex differences in adaptations to resistance training are apparent in older adults. However, it is evident that the interpretation of sex-dependent adaptations to resistance training is heavily influenced by the presentation of the results in either an absolute or relative context.

STUDY REGISTRATION

Open Science Framework (osf.io/afn3y/).

The Effect of Resistance Training in Women on Dynamic Strength and Muscular Hypertrophy: A Systematic Review with Meta-analysis

BACKGROUND

The effect of resistance training (RT) on adaptations in muscular strength and hypertrophy has never been examined in an exclusively female synthesis of the literature.

OBJECTIVE

The objectives of this study were threefold: (1) to systematically review the literature on female adaptations to RT, characterising the effect in terms of muscular strength and hypertrophy; (2) to distinguish the individual effects of intervention duration, frequency, and intensity on these adaptations via sub-analysis; (3) to draw evidence-based conclusions regarding training expectations in female populations.

METHODS

Three electronic databases were searched using terms related to RT combined with females or women. Random-effects meta-analyses were undertaken to estimate the effect of RT on muscular strength and hypertrophy in females. Possible predictors that may have influenced training-related effects (e.g., training intensity and volume) were explored using univariate analyses.

RESULTS

The systematic search identified 14,067 articles of which a total of 24 studies met the inclusion criteria and were eligible. Upper body strength was assessed in 15 studies, lower body strength in 19 studies, and muscular hypertrophy in 15 studies. Study duration lasted between 4 weeks and 12 months. Large-effect sizes were found for upper body strength (Hedges' g = 1.70; p < 0.001) and lower body strength (Hedges' g = 1.40; p < 0.001). Following use of the Trim and Fill method (due to presence of publication bias), a large effect still remained for upper body strength (Hedges' g = 1.07), although a medium effect was found for lower body strength (Hedges' g = 0.52). A medium effect was found for muscular hypertrophy (g = 0.52, p = 0.002). Sub-analyses revealed that the moderating variables "training frequency" and "training volume" significantly influenced lower body muscular strength (p < 0.001). "Training frequency" and "sets per exercise" moderated the RT effects on upper body strength (p < 0.01). No moderating variables were found to significantly influence muscular hypertrophy. A trend for a moderating effect on upper body strength was found for "age of participants" (p = 0.08), whereby younger participants experienced a greater effect. A moderating effect was also observed where supervised training had a larger influence on the adaptation of lower body strength (p = 0.05) compared with unsupervised training. Methodological quality for the studies included in the review was found to be moderate.

CONCLUSIONS

RT elicits large improvements in muscular strength and hypertrophy in healthy adult females. Training volume and frequency appear to be important variables that influence muscular strength.

Changes in Fatigue Are the Same for Trained Men and Women after Resistance Exercise

PURPOSE

To measure changes in fatigue and knee-extensor torque in the 48 h after trained men and women completed a full-body resistance exercise session.

METHODS

Eight trained women (mean ± SD: age, 25.6 ± 5.9 yr; height, 1.68 ± 0.06 m; mass, 71.0 ± 8.6 kg) and eight trained men (age, 25.5 ± 6.2 yr; height, 1.79 ± 0.05 m; mass, 86.4 ± 9.8 kg) performed a full-body resistance exercise session based on real-world athletic practice. Measurements were performed before and after the exercise session, as well as 1, 24, and 48 h after the session. Fatigue and pain were measured with standardized self-report measures. Maximal isometric contractions with the knee extensors and superimposed femoral nerve stimulation were performed to examine maximal torque, rate of torque development, voluntary activation, and muscle contractility. Two sets of 10 isokinetic contractions (60°·s) with the knee extensors were performed during the protocol with use of near-infrared spectroscopy to assess muscle oxygenation. EMG were recorded from two quadriceps muscles during all isometric and isokinetic contractions.

RESULTS

Fatigue was increased from baseline for both sexes until 48 h after training (P < 0.001). Maximal torque and evoked twitch amplitudes were similarly reduced after exercise for men and women (P < 0.001). Voluntary activation and EMG amplitudes were unchanged after the training session. Muscle oxygenation was 13.3% ± 17.4% (P = 0.005) greater for women during the isokinetic repetitions, and the values were unchanged after the training session.

CONCLUSIONS

This is the first study to show similar changes in the fatigue reported by trained men and women in the 48 h after a training session involving full-body resistance exercises. Sex differences in muscle oxygenation during exercise do not influence the reductions in muscle force, activation, or contractility after the training session.

Differential changes in muscle architecture and neuromuscular fatigability induced by isometric resistance training at short and long muscle-tendon unit lengths

We evaluated the effects of differential muscle architectural adaptations on neuromuscular fatigue resistance. Seven young males and six females participated in this study. Using a longitudinal within-subject design, legs were randomly assigned to perform isometric training of the tibialis anterior (TA) three times per week for 8 wk at a short (S-group) or long muscle-tendon unit length (L-group). Before and following training, fascicle length (FL) and pennation angle (PA) of the TA were assessed. As well, fatigue-related time course changes in isometric maximal voluntary contraction (MVC) torque and isotonic peak power (20% MVC resistance) were determined before, immediately after, and 1, 2, 5, and 10 min following task failure. The fatiguing task consisted of repeated maximal effort isotonic (20% MVC resistance) contractions over a 40° range of motion until the participant reached a 40% reduction in peak power. Although there was no clear improvement in neuromuscular fatigue resistance following training in either group (P = 0.081; S-group: ∼20%; L-group: ∼51%), the change in neuromuscular fatigue resistance was related positively to the training-induced increase in PA (∼6%, P < 0.001) in the S-group (r = 0.739, P = 0.004) and negatively to the training-induced increase in FL (∼4%, P = 0.001) in the L-group (r = -0.568, P = 0.043). Both groups recovered similarly for MVC torque and peak power after the fatiguing task as compared with before training. We suggest that the relationships between the changes in muscle architecture and neuromuscular fatigue resistance depend on the muscle-tendon unit lengths at which the training is performed.NEW & NOTEWORTHY Eight weeks of isometric training at a long or short muscle-tendon unit length increased and did not change fascicle length, respectively. The "width" of the torque-angle relationship plateau became broader following isometric training at the long length. Despite marked differences in muscle architecture and functional adaptations between the groups, there was only a small-magnitude improvement in neuromuscular fatigue resistance, which was surprisingly negatively related to increased fascicle length in the long length-training group.

Changes in the quadriceps spinal reflex pathway after repeated sprint cycling are not influenced by ischemic preconditioning

PURPOSE

We examined the effect of ischemic preconditioning (IPC) on changes in muscle force, activation, and the spinal reflex pathway during and after repeated sprint cycling.

METHODS

Eight recreationally active men (high-intensity cardiorespiratory training > 3 times per week, > 6 months) completed two exercise sessions (5 sets of 5 cycling sprints, 150% max W), preceded by either IPC (3 × 5 min leg occlusions at 220 mmHg) or SHAM (3 × 5 min at 20 mmHg). Knee extensor maximal force and rate of force were measured before (PRE), immediately post (POST), 1H, and 24H after cycling. Twitch interpolation and resting potentiated twitches were applied to estimate voluntary activation and muscle contractility, respectively. Quadriceps H-reflex recruitment curves were collected at all time-points using 10 Hz doublet stimulation to allow estimation of H-reflex post-activation depression. Surface electromyograms and tissue oxygenation (via near-infrared spectroscopy) were continuously recorded during cycling.

RESULTS

IPC did not affect any measure of neuromuscular function or performance during cycling. Maximal force and muscle contractility were significantly lower at POST and 1H compared to PRE and 24H by up to 50% (p < 0.01). Maximal force was lower than PRE at 24H by 8.7% (p = 0.028). Voluntary activation and rate of force were unchanged. A rightwards shift was observed for the H-reflex recruitment curve POST, and post-activation depression was higher than all other time-points at 24H (p < 0.05). Muscle activation and oxygenation decreased during cycling.

CONCLUSIONS

IPC has a nominal effect on mechanisms associated with neuromuscular function during and after exercise in healthy populations.