Isokinetic eccentric resistance training prevents loss in mechanical muscle function after running

Prediction of instantaneous perceived effort during outdoor running using accelerometry and machine learning

The rate of perceived effort (RPE) is a subjective scale widely used for defining training loads. However, the subjective nature of the metric might lead to an inaccurate representation of the imposed metabolic/mechanical exercise demands. Therefore, this study aimed to predict the rate of perceived exertions during running using biomechanical parameters extracted from a commercially available running smartwatch. Forty-three recreational runners performed a simulated 5-km race on a track, providing their RPE from a Borg scale (6-20) every 400 m. Running distance, heart rate, foot contact time, cadence, stride length, and vertical oscillation were extracted from a running smartwatch (Garmin 735XT). Machine learning regression models were trained to predict the RPE at every 5 s of the 5-km race using subject-independent (leave-one-out), as well as a subject-dependent regression method. The subject-dependent method was tested using 5%, 10%, or 20% of the runner's data in the training set while using the remaining data for testing. The average root-mean-square error (RMSE) in predicting the RPE using the subject-independent method was 1.8 ± 0.8 RPE points (range 0.6-4.1; relative RMSE ~ 12 ± 6%) across the entire 5-km race. However, the error from subject-dependent models was reduced to 1.00 ± 0.31, 0.66 ± 0.20 and 0.45 ± 0.13 RPE points when using 5%, 10%, and 20% of data for training, respectively (average relative RMSE < 7%). All types of predictions underestimated the maximal RPE in ~ 1 RPE point. These results suggest that the data accessible from commercial smartwatches can be used to predict perceived exertion, opening new venues to improve training workload monitoring.

Muscle Fatigue Is Attenuated When Applying Intermittent Compared With Continuous Blood Flow Restriction During Endurance Cycling

PURPOSE

The aim of this study was to identify a blood-flow-restriction (BFR) endurance exercise protocol that maximizes metabolic strain and minimizes muscle fatigue.

METHODS

Twelve healthy participants accomplished 5 different interval cycling endurance exercises (2-min work, 1-min rest) in a randomized order: (1) control, low intensity with unrestricted blood flow (CON30); (2) low intensity with intermittent BFR (i-BFR30, ∼150 mm Hg); (3) low intensity with continuous BFR (c-BFR, ∼100 mm Hg); (4) unloaded cycling with i-BFR0 (∼150 mm Hg); and (5) high intensity (HI) with unrestricted blood flow. Force production, creatine kinase activity, antioxidant markers, blood pH, and potassium (K+) were measured in a range of 5 minutes before and after each cycling exercise protocol.

RESULTS

HI showed the highest reduction (Δ = -0.26 [0.05], d = 5.6) on blood pH. Delta pH for c-BRF30 (Δ = -0.02 [0.03], d = 0.8) and Δ pH for i-BRF30 (Δ = -0.04 [0.03], d = 1.6) were different from each other, and both were higher compared with CON30 (Δ = 0.03 [0.03]). There was significant before-to-after force loss following HI (Δ = 55 [40] N·m-1, d = 1.5) and c-BFR30 (Δ = 27 [21] N·m-1, d = 0.7) protocols only, which were accompanied by significant increases in K+ (HI: Δ = 0.94 [0.65] mmol·L-1, d = 1.8; c-BFR30: Δ = 0.72 [0.85] mmol·L-1, d = 1.2). Moreover, all BFR conditions elicited slight increases in plasma creatine kinase, but not for HI and CON30. Glutathione changes from before to after were significant for all BFR conditions and HI, but not for CON30.

CONCLUSIONS

The attenuation in fatigue-induced reductions in maximal force suggests that i-BFR exercise could be preferable to c-BFR in improving exercise capacity, with considerably less biologic stress elicited from HI exercises.

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.

A single bout of downhill running attenuates subsequent level running-induced fatigue

Fatigue can be defined as exercise-induced strength loss. During running, fatigue can be partially explained by repetitive low-intensity eccentric contractions-induced muscle damage (EIMD). Previous studies showed that a bout of downhill running (DR) attenuated subsequent EIMD. Thus, we tested if a 30-min DR bout would attenuate fatigue induced by subsequent 60-min level running (LR). Twenty-seven male college students were randomly allocated to an experimental (EXP) or a control (CON) group. All participants performed LR on a treadmill at 70% of the velocity (vVO₂peak) corresponding to peak oxygen uptake (VO₂peak). Only EXP performed a 30-min DR (− 15%) on a treadmill at 70% vVO₂peak fourteen days before LR. Indirect EIMD markers and neuromuscular function were assessed before, immediately and 48 h after DR and LR. Knee extension isometric peak torque (IPT) decreased (− 36.3 ± 26%, p < 0.05) immediately following DR with full recovery reached 48 h post-DR. Muscle soreness developed (p < 0.05) immediately (37 ± 25 mm) and 48 h (45 ± 26 mm) post-DR. IPT and rate of torque development (RTD) at late phases (> 150 ms) from the onset of muscle contraction decreased significantly (− 10.7 ± 6.1% and from − 15.4 to − 18.7%, respectively) immediately after LR for the CON group and remained below baseline values (− 5.6 ± 8.5% and from − 13.8 to − 14.9%, respectively) 48 h post-LR. However, IPT and late RTD were not significantly affected by LR for the EXP group, showing a group x time interaction effect. We concluded that a single DR bout can be used to attenuate fatigue induced by a LR performed fourteen days after.

Fatigue-related changes in vertical impact properties during normal and silent running

Running while minimizing sound volume can reduce vertical impact loading, potentially reducing injury risks. Fatigue can increase the vertical loading rate during running, but it is unknown whether fatigue influences silent running similarly. This study aimed to explore the differences in vertical impact properties during normal and silent running following a fatiguing task. Seventeen participants performed overground running (normal and silent) before and after a fatiguing running protocol. Running footfall sounds were collected using four microphones surrounding a force platform on the track. Peak impact sound, vertical impact peak force (IPF), instantaneous (VILR), and average vertical loading rate (VALR) were compared from Pre- to Post-fatigue. Peak impact sounds were significantly greater for fatigued runners during normal running when compared to silent running (p < 0.005), without changes in force parameters. Moreover, peak impact sounds, IPF, VILR, and VALR from normal running were greater when compared to silent running (p < 0.001), both fresh or fatigued. Our results suggest that fatigue may not compromise silent running technique, which may be relevant to reduce early vertical impact loading. Therefore, runners seeking to modify running style towards the reduction of impact loading may benefit from including silent running drills in their training sessions.

Recovery of Force-Time Characteristics After Australian Rules Football Matches: Examining the Utility of the Isometric Midthigh Pull

Purpose: This study assessed the utility of force-time characteristics from the isometric midthigh pull (IMTP) as a measure of neuromuscular function after elite-level Australian rules football matches. It was hypothesized that rate characteristics of force development would demonstrate a different response magnitude and recovery time course than peak force measurements. Methods: Force-time characteristics of the IMTP (peak force, 0- to 50-ms rate of force development [RFD], 100- to 200-ms RFD) were collected at 48 (G+2), 72 (G+3), and 96 h (G+4) after 3 competitive Australian rules football matches. Results: Meaningful reductions (>75% of the smallest worthwhile change) were observed at G+2, G+3, and G+4 for RFD 0-50 milliseconds (-25.8%, -17.5%, and -16.9%) and at G+2 and G+3 for RFD 100-200 milliseconds (-15.7% and -11.7%). No meaningful reductions were observed for peak force at any time point (G+2 -4.0%, G+3 -3.9%, G+4 -2.7%). Higher week-to-week variation was observed for RFD 0-50 milliseconds (G+2 17.1%, G+3 27.2%, G+4 19.3%) vs both RFD 100-200 milliseconds (G+2 11.3%, G+3 11.5%, G+4 7.2%) and peak force (G+2 4.8%, G+3 4.4%, G+4 8.4%). Conclusions: These findings highlight the potential use of rate characteristics from the IMTP as measures of neuromuscular function in elite sport settings, and in particular RFD 100-200 milliseconds due to its higher reliability. Interestingly, peak force collected from the IMTP was not meaningfully suppressed at any time point after elite Australian rules football match play. This suggests that rate characteristics from IMTP may provide more sensitive and valuable insight regarding neuromuscular function recovery kinetics than peak measures.

Neuromuscular Fatigue Does Not Impair the Rate of Force Development in Ballistic Contractions of Submaximal Amplitudes

The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or near-maximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (-12, -12, -21, and -19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.

Hamstrings-to-quadriceps strength and size ratios of male professional soccer players with muscle imbalance

The aim of this study was to determine the correlation between the concentric hamstrings/quadriceps muscle strength (Hcon :Qcon ) and cross-sectional area ratios (Hcsa :Qcsa ) in professional soccer players with Hcon :Qcon imbalance. Nine male professional soccer players (25·3 ± 4·1 years) performed five maximal concentric contractions of the knee extensors (KE) and flexors (KF) at 60 s(-1) to assess Hcon :Qcon . The test was performed using the dominant (preferred kicking), and non-dominant limb with a 5-min recovery period was allowed between them. Only players with Hcon :Qcon < 0·60 (range: 0·45-0·59) in both limbs were included in this study. The muscle cross-sectional area (CSA) of KE and KF was determined by magnetic resonance imaging. The correlations between Hcon :Qcon and Hcsa :Qcsa in the dominant leg (r = -0·33), non-dominant leg (r = 0·19) and in the both legs combined (r = 0·28) were not statistically significant (P>0·05). Thus, the Hcon :Qcon seems not to be determined by Hcsa :Qcsa in professional soccer players with Hcon :Qcon imbalance.

Early-phase musculoskeletal adaptations to different levels of eccentric resistance after 8 weeks of lower body training

PURPOSE

Eccentric muscle actions are important to the development of muscle mass and strength and may affect bone mineral density (BMD). This study's purpose was to determine the relative effectiveness of five different eccentric:concentric load ratios to increase musculoskeletal parameters during early adaptations to resistance training.

METHODS

Forty male subjects performed a supine leg press and calf press training program 3 days week(-1) for 8 weeks. Subjects were matched for pre-training leg press 1-repetition maximum strength (1-RM) and randomly assigned to one of five training groups. Concentric training load (% 1-RM) was constant across groups, but within groups, eccentric load was 0, 33, 66, 100, or 138% of concentric load. Muscle mass (dual energy X-ray absorptiometry; DXA), strength (1-RM), and BMD (DXA) were measured pre- and post-training. Markers of bone metabolism were assessed pre-, mid- and post-training.

RESULTS

The increase in leg press 1-RM in the 138% group (20 ± 4%) was significantly greater (P < 0.05) than the 0% (8 ± 3%), 33% (8 ± 5%) and 66% (8 ± 4%) groups, but not the 100% group (13 ± 6 %; P = 0.15). All groups, except the 0% group, increased calf press 1-RM (P < 0.05). Leg lean mass and greater trochanter BMD were increased only in the 138% group (P < 0.05).

CONCLUSIONS

Early-phase adaptations to eccentric overload training include increases in muscle mass and site-specific increases in BMD and muscle strength which are not present or are less with traditional and eccentric underload training. Eccentric overload provides a robust musculoskeletal stimulus that may benefit bedridden patients, individuals recovering from injury or illness, and astronauts during spaceflight.

Rate of force development as a measure of muscle damage

This study tested the hypothesis that rate of force development (RFD) would be a more sensitive indirect marker of muscle damage than maximum voluntary isometric contraction (MVC) peak torque. Ten men performed one concentric cycling and two eccentric cycling (ECC1, ECC2) bouts for 30 min at 60% of maximal concentric power output with 2 weeks between bouts. MVC peak torque, RFD, and vastus lateralis electromyogram amplitude and mean frequency were measured during a knee extensor MVC before, immediately after and 1-2 days after each bout. The magnitude of decrease in MVC peak torque after exercise was greater (P < 0.05) for ECC1 (11-25%) than concentric cycling (2-12%) and ECC2 (0-16%). Peak RFD and RFD from 0-30 ms, 0-50 ms, 0-100 ms, to 0-200 ms decreased (P < 0.05) immediately after all cycling bouts without significant differences between bouts, but RFD at 100-200 ms interval (RFD(100-200)) decreased (P < 0.05) at all time points after ECC1 (24-32%) and immediately after ECC2 (23%), but did not change after CONC. The magnitude of decrease in RFD(100-200) was 7-19% greater than that of MVC peak torque after ECC1 (P < 0.05). It is concluded that RFD(100-200) is a more specific and sensitive indirect marker of eccentric exercise-induced muscle damage than MVC peak torque.

Muscle conduction velocity, strength, neural activity, and morphological changes after eccentric and concentric training

This study compared the effects of concentric and eccentric training on neuromuscular adaptations in young subjects. Twenty-two men and women were assigned to one of two groups: concentric (CON, n = 11) and eccentric (ECC, n = 11) training. Training consisted of 6 weeks of isokinetic exercise, performed twice weekly, starting with two sets of eight repetitions, and progressing to five sets of 10 repetitions. Subjects were tested in strength variables [concentric, eccentric, and isometric peak torque (PT), and rate of force development (RFD)], muscle conduction velocity (CV), neuromuscular activity, vastus lateralis (VL) muscle thickness, and echo intensity as determined by ultrasonography. There were similar increases in the concentric and eccentric PTs in both the CON and ECC groups (P < 0.01), but only the ECC group showed an increase in isometric PT (P < 0.001). Similarly, both groups exhibited increased VL muscle thickness, CV, and RFD, and reduced VL echo intensity (P < 0.05). Significant correlations were observed among the relative changes in the neuromuscular outcomes and training variables (e.g., total work, average PT) (r = 0.68-0.75, P < 0.05). The results showed that both training types similarly improved dynamic PT, CV, RFD, and muscle thickness and quality during the early weeks of training.