Disparate Mechanisms of Fatigability in Response to Prolonged Running versus Cycling of Matched Intensity and Duration

Durability in recreational runners: effects of 90-min low-intensity exercise on the running speed at the lactate threshold

PURPOSE

Recent studies have suggested that the capability to resist deterioration of physiological characteristics could be an independent factor contributing to endurance performance. This study aimed at investigating whether prolonged low-intensity exercise induces shifts in the lactate threshold, and whether fatigue-induced changes differ between the sexes.

METHODS

A total of 31 (15 females) recreational runners performed an incremental treadmill test and a 90-min low-intensity exercise (LIT90) on two separate occasions. The LIT90 was performed at 90% of the first lactate threshold speed (LT1v), derived from the incremental treadmill test. The LT1v was determined from a 5-stage (3 min) submaximal threshold test (SubmaxLT), performed before and after LIT90. The SubmaxLTs were followed by a 10/5 reactivity jump test. Respiratory gases, heart rate (HR), and HR-derived detrended fluctuation analysis alpha 1 (DFA-a1) were assessed every 15 min during the LIT90.

RESULTS

A significant decrease (p < 0.01) was observed in the LT1v in females (- 5.8 ± 4.4%) and in males (- 5.3 ± 6.4%). The HR increased (p < 0.001) similarly in females (5.9 ± 3.1%) and in males (5.5 ± 3.6%) during the LIT90, while energy expenditure increased (3.1 ± 4.5%, p = 0.013) in females but remained unchanged in males (0.9 ± 3.1%). Change in DFA-a1 during the LIT90 was the only marker that correlated significantly with the relative change of LT1v (r = 0.463, p = 0.013).

CONCLUSION

LIT90 induced significant decreases in the LT1v, and the changes were comparable between sexes. DFA-a1 could be a potential intra-session marker of durability.

The fourth dimension: physiological resilience as an independent determinant of endurance exercise performance

Endurance exercise performance is known to be closely associated with the three physiological pillars of maximal O2 uptake (V ̇ O 2 max $\dot{V}_{{\rm O}_{2}{\rm max}}$ ), economy or efficiency during submaximal exercise, and the fractional utilisation ofV ̇ O 2 max $\dot{V}_{{\rm O}_{2}{\rm max}}$ (linked to metabolic/lactate threshold phenomena). However, while 'start line' values of these variables are collectively useful in predicting performance in endurance events such as the marathon, it is not widely appreciated that these variables are not static but are prone to significant deterioration as fatiguing endurance exercise proceeds. For example, the 'critical power' (CP), which is a composite of the highest achievable steady-state oxidative metabolic rate and efficiency (O2 cost per watt), may fall by an average of 10% following 2 h of heavy intensity cycle exercise. Even more striking is that the extent of this deterioration displays appreciable inter-individual variability, with changes in CP ranging from <1% to ∼32%. The mechanistic basis for such differences in fatigue resistance or 'physiological resilience' are not resolved. However, resilience may be important in explaining superlative endurance performance and it has implications for the physiological evaluation of athletes and the design of interventions to enhance performance. This article presents new information concerning the dynamic plasticity of the three 'traditional' physiological variables and argues that physiological resilience should be considered as an additional component, or fourth dimension, in models of endurance exercise performance.

Performance and perceived fatigability across the intensity spectrum: role of muscle mass during cycling

The role of muscle mass in modulating performance and perceived fatigability across the entire intensity spectrum during cycling remains unexplored. We hypothesized that at task failure (Tlim), muscle contractile function would decline more following single- (SL) versus double-leg (DL) cycling within severe and extreme intensities, but not moderate and heavy intensities. After DL and SL ramp-incremental tests, on separate days, 11 recreationally active males (V̇o2max: 49.5 ± 7.7 mL·kg-1·min-1) completed SL and DL cycling until Tlim within each intensity domain. Power output for SL trials was set at 60% of the corresponding DL trial. Before and immediately after Tlim, participants performed an isometric maximal voluntary contraction (MVC) coupled with one superimposed and three resting femoral nerve stimulations [100 Hz; 10 Hz; single twitch (Qtw)] to measure performance fatigability. Perceived fatigue, leg pain, dyspnea, and effort were collected during trials. Tlim within each intensity domain was not different between SL and DL (all P > 0.05). MVC declined more for SL versus DL following heavy- (-42 ± 16% vs. -30 ± 18%; P = 0.011) and severe-intensity cycling (-41 ± 12% vs. -31 ± 15%; P = 0.036). Similarly, peak Qtw force declined more for SL following heavy- (-31 ± 12% vs. -22 ± 10%; P = 0.007) and severe-intensity cycling (-49 ± 13% vs. -40 ± 7%; P = 0.048). Except for heavy intensity, voluntary activation reductions were similar between modes. Similarly, except for dyspnea, which was lower for SL versus DL across all domains, ratings of fatigue, pain, and effort were similar at Tlim between exercise modes. Thus, the amount of muscle mass modulates the extent of contractile function impairment in an intensity-dependent manner.NEW & NOTEWORTHY We investigated the modulatory role of muscle mass on performance and perceived fatigability across the entire intensity spectrum. Despite similar time-to-task failure, single-leg cycling resulted in greater impairments in muscle contractile function within the heavy- and severe-intensity domains, but not the moderate- and extreme-intensity domains. Perceived fatigue, pain, and effort were similar between cycling modes. This indicates that the modulatory role of muscle mass on the extent of performance fatigability is intensity domain-dependent.

Exacerbated impairments in neuromuscular function when two bouts of team sport match simulations are separated by 48 h

Intermittent team sports, involving high metabolic and mechanical demands, elicit prolonged impairments in neuromuscular function which persist for ∼48-72 h. Whether impairments in neuromuscular function are exacerbated when such exercise is repeated with incomplete recovery is unknown. This study assessed the neuromuscular, heart rate and metabolic responses to two bouts of ∼90 min modified team sport match simulations separated by 48 h in 12 competitive football players. Before and 2 min after both bouts, knee extensor isometric maximal voluntary contraction (MVC), contractile function (Qtw,pot ) and voluntary activation (VA) were measured. Heart rate (HR), sprint time, blood lactate and glucose were measured throughout both bouts. MVC was reduced relative to baseline at post-bout 1 (21 ± 12%; P = 0.003) and pre-bout 2 (14 ± 11%; P = 0.009), and was lower post-bout 2 (33 ± 14%; P < 0.001) relative to post-bout 1 (P = 0.036). Qtw,pot was reduced post-bout 1 (30 ± 11%; P < 0.001) and pre-bout 2 (9 ± 6%; P = 0.004), and was not different post-bout 2 (28 ± 8%; P < 0.001) relative to post-bout 1 (P = 0.872). VA was reduced post-bout 1 (8 ± 7%; P = 0.023), recovered pre-bout 2 (P = 0.133) and was lower post-bout 2 (16 ± 7%; P < 0.001) relative to post-bout 1 (P = 0.029). Total sprint time was longer, and HR, blood lactate and glucose were lower during bout 2 than bout 1 (P ≤ 0.021). Thus, impairments in neuromuscular function are exacerbated when high-intensity intermittent exercise is performed with incomplete recovery concurrent with accentuated reductions in VA. The lower blood lactate and glucose during the second bout might be due, at least in part, to reduced glycogen availability upon commencing exercise and consequently a greater reliance on glucose extraction. NEW FINDINGS: What is the central question of this study? There is limited evidence on whether impairments in neuromuscular function are exacerbated when prolonged high-intensity intermittent exercise is repeated with incomplete recovery: what are the neuromuscular consequences of performing two bouts of a modified team sport match simulations separated by 48 h? What is the main finding and its importance? Impairments in knee extensor force generating capacity are exacerbated concurrent with accentuated reductions in nervous system activation of muscle when prolonged high-intensity intermittent exercise is repeated with 48 h recovery.

The proportional distribution of training by elite endurance athletes at different intensities during different phases of the season

The present review examines retrospective analyses of training intensity distribution (TID), i.e., the proportion of training at moderate (Zone 1, Z1), heavy (Z2) and severe (Z3) intensity by elite-to-world-class endurance athletes during different phases of the season. In addition, we discuss potential implications of our findings for research in this field, as well as for training by these athletes. Altogether, we included 175 TIDs, of which 120 quantified exercise intensity on the basis of heart rate and measured time-in-zone or employed variations of the session goal approach, with demarcation of zones of exercise intensity based on physiological parameters. Notably, 49% of the TIDs were single-case studies, predominantly concerning cross-country skiing and/or the biathlon. Eighty-nine TIDs were pyramidal (Z1 > Z2 > Z3), 65 polarized (Z1 > Z3 > Z2) and 8 "threshold" (Z2 > Z1 = Z3). However, these relative numbers varied between sports and the particular phases of the season. In 91% (n = 160) of the TIDs >60% of the endurance exercise was of low intensity. Regardless of the approach to quantification or phase of the season, cyclists and swimmers were found to perform a lower proportion of exercise in Z1 (<72%) and higher proportion in Z2 (>16%) than athletes involved in the triathlon, speed skating, rowing, running, cross-country skiing or biathlon (>80% in Z1 and <12% in Z2 in all these cases). For most of the athletes their proportion of heavy-to-severe exercise was higher during the period of competition than during the preparatory phase, although with considerable variability between sports. In conclusion, the existing literature in this area does not allow general conclusions to be drawn. The methods utilized for quantification vary widely and, moreover, contextual information concerning the mode of exercise, environmental conditions, and biomechanical aspects of the exercise is often lacking. Therefore, we recommend a more comprehensive approach in connection with future investigations on the TIDs of athletes involved in different endurance sports.

Shorter High-Intensity Cycling Intervals Reduce Performance and Perceived Fatigability at Work-Matched but Not Task Failure

INTRODUCTION

The intensity, duration, and distribution of work and recovery phases during high-intensity interval training (HIIT) modulate metabolic perturbations during exercise and subsequently influence the development of performance fatigability and exercise tolerance. This study aimed to characterize neuromuscular, perceptual, and cardiorespiratory responses to work-to-rest ratio-matched HIIT protocols differing in work and rest interval duration.

METHODS

Twelve healthy individuals (six women) first completed a ramp incremental test to determine 90% of peak power output, and then in three randomized visits, they completed three cycling protocols to task failure at 90% of peak power output: (i) 3- to 3-min work-to-passive rest ratio HIIT (HIIT 3min ), (ii) 1- to 1-min work-to-passive rest ratio HIIT (HIIT 1min ), and (iii) constant load (CL). Interpolated twitch technique, including maximal voluntary isometric knee extensions and femoral nerve electrical stimuli, was performed at baseline, every 6 min of work, and task failure. Perceptual and cardiorespiratory responses were recorded every 3 min and continuously across the exercises, respectively.

RESULTS

The work completed during HIIT 1min (8447 ± 5124 kJ) was considerably greater than HIIT 3min (1930 ± 712 kJ) and CL (1076 ± 356) ( P < 0.001). At work-matched, HIIT 1min resulted in a lesser decline in maximal voluntary contraction and twitch force compared with HIIT 3min and CL ( P < 0.001). Perceived effort, pain, and dyspnea were least in HIIT 1min and HIIT 3min compared with CL ( P < 0.001). At task failure, HIIT 1min resulted in less voluntary activation than HIIT 3min ( P = 0.010) and CL ( P = 0.043), and engendered less twitch force decline than CL ( P = 0.021).

CONCLUSIONS

Overall, the mitigated physiological and perceptual responses during shorter work periods (HIIT 1min ) enhance exercise tolerance in comparison to longer work intervals at the same intensity (HIIT 3min , CL).

Changes in Cost of Locomotion Are Higher after Endurance Cycling Than Running When Matched for Intensity and Duration

INTRODUCTION

Cost of locomotion (C L ) has been shown to increase after endurance running and cycling bouts. The main purpose of this study was to compare, in the same participants, the effect of both modalities on C L when matched for relative intensity and duration.

METHODS

Seventeen recreational athletes performed two incremental tests in running and cycling to determine the first ventilatory threshold then two 3-h bouts of exercise at 105% of threshold, with gas exchange measurements taken for 10 min at the start, middle and end of the 3 h to calculate C L . Neuromuscular fatigue during isometric knee extensor contractions and force-velocity profile on a cycle ergometer were assessed before and immediately after the 3-h trials.

RESULTS

C L significantly increased at mid (+3.7%, P = 0.006) and end (+7.4%, P < 0.001) of exercise for cycling compared with start, whereas it did not change with time for running. Cardio-respiratory and metabolic variables changed similarly for cycling and running, therefore not explaining the time-course differences in C L between modalities. Changes in C L during cycling correlated significantly with loss of maximal force extrapolated from the force-velocity profile ( r = 0.637, P = 0.006) and changes in cadence ( r = 0.784, P < 0.001).

CONCLUSIONS

The type of locomotion influences the effects of exercise on energy cost because 3 h of exercise at the same relative intensity caused a significant increase of cycling C L , and no changes in running C L . The changes in C L in cycling are likely due, at least in part, to fatigue in the locomotor muscles.

Influence of Torque and Cadence on Power Output Production in Cyclists

PURPOSE

No information is available on the torque/cadence relationship in road cyclists. We aimed to establish whether this relationship differs between cyclists of different performance levels or team roles.

METHODS

Mean maximal power (MMP) output data from 177 riders were obtained from 2012 to 2021 from training and competitions. Cyclists were categorized according to their performance level (world-tour [WT, n = 68], procontinental [PC, n = 63], or under 23 [U23, n = 46]) and team role (time trialists [n = 12], all-rounders [n = 94], climbers [n = 64], or team leaders [n = 7]).

RESULTS

A significant interaction effect was found for absolute and relative MMP (P < .001), with higher values in PC than WT for short (5-60 s) efforts and the opposite trend for longer durations. MMP was also greater in PC than in U23 for short efforts (30-60 s), with WT and PC attaining higher MMP than U23 for longer bouts (5-60 min). A significant interaction effect was found for cadence (P = .007, but with no post hoc differences) and absolute (P = .010) and relative torque (P = .002), with PC and WT showing significantly higher torque (all P < .05) than U23 for 5- to 60-minute efforts, yet with no differences between the former 2 performance levels. No interaction effect between team roles was found for cadence (P = .185) or relative torque (P = .559), but a significant interaction effect was found for absolute torque (P < .001), with all-rounders attaining significantly higher values than climbers for 5-second to 5-minute efforts.

CONCLUSIONS

Differences in MMP between cycling performance levels and rider types are dependent on torque rather than cadence, which might support the role of torque development in performance.

The completely recover of quadriceps muscle peripheral fatigue after running in Olympic but not in Sprint triathlon

ABSTRACTThis study compared central and peripheral fatigue development between Sprint and Olympic distance triathlon. Fifteen male triathletes performed Sprint and Olympic triathlon simulations in a randomized and counterbalanced order. Central and peripheral fatigue was evaluated from changes in voluntary activation level (VAL) and twitch responses of quadriceps muscle (Q_tw,pot), respectively. Q_tw,pot reduced from baseline to post-swimming similarly between triathlon simulations (Sprint, -17±11%; Olympic, -13±9%). In post-cycling, Q_tw,pot further declined to a similar extent between triathlon distances (Sprint, -31±15%; Olympic, -28±11%). In post-running, Q_tw,pot was fully recovered in Olympic triathlon (-4±10%), whereas there was only a partial recovery of Q_tw,pot in Sprint triathlon (-20±11%). VAL was not reduced in post-swimming, but reduction was similar between triathlon distances in post-cycling (Sprint, -10±9%; Olympic, -8±8%) and post-running (Sprint, -15±14%; Olympic, -16±8%). In Sprint triathlon, the swimming speed (1.07±0.13 m ·s^-1) was above (p<.001) critical speed (1.01±0.14 m ·s^-1), the cycling power (179.7±27.2W) was below the respiratory compensation point (216.3±27.8W, p<.001) and running speed (13.7±1.05km·h^-1) similar to the respiratory compensation point (13.2±0.70 km·h^-1, p=.124). In Olympic triathlon, swimming speed (1.03±0.13m·s^-1) was similar to critical speed (p=.392), and both cycling power (165.3±27.3W) and running speed (12.6±1.05km·h^-1) were below the respiratory compensation point (p≤.007). In conclusion, peripheral fatigue progressed until post-cycling regardless of triathlon distances. However, peripheral fatigue was fully recovered after running in Olympic but not in Sprint triathlon. The central fatigue started in post-cycling and progressed until post-running regardless of triathlon distances.