The effects of eccentric exercise on motor performance in young and older women

The purpose of the present study was to determine if old individuals show a greater exercise-induced decrement in motor performance and slower recovery compared to young individuals. Ten college-age women (23.6 years) and ten older women (67.4 years) performed an exercise consisting of 24 eccentric actions of the forearm flexors. In young subjects, eccentric exercise is known to produce repairable muscle damage. Before the exercise and for 5 days after, isometric strength, soreness, reaction time, and movement time were measured. For both groups, strength was reduced and soreness developed in the days following the exercise, generally indicating that muscle damage had occurred. The older subjects showed a slower strength recovery such that by 5 days after exercise they had not returned to their initial level of strength. There was no significant difference in soreness development between groups. Reaction time and movement time were not adversely affected by the exercise. Thus, the older subjects demonstrated a slower strength recovery after damage-inducing exercise, and, with regard to response speed, the older subjects could compensate for the impaired muscle function as well as the younger subjects.     

Circadian organization in a diurnal rodent, Arvicanthis ansorgei Thomas 1910: chronotypes, responses to constant lighting conditions, and photoperiodic changes

Little information is available on circadian organization in diurnal mammals. In the present study, the daily patterns of wheel-running activity were described in a diurnal rodent, Arvicanthis ansorgei Thomas 1910, as assessed by karyological analysis. Among 108 animals born in the colony and studied under a 12:12 light-dark cycle (lights on at 7:00 a.m.), the authors determined the timing of daily activity (i.e., mean onsets and offsets of pattern of locomotor activity) and the level of wheel-running activity performed during daytime versus nighttime. The activity pattern was essentially diurnal in 84% of individuals, 46% being active only during the light period +/- 1 h (activity onsets and offsets at 6:20 a.m. and 7:40 p.m., respectively) and 38% being diurnal with a period of nocturnal activity longer than 1 h (activity onsets and offsets at 5:40 a.m. and 9:30 p.m., respectively). Of the 108 animals, 16% expressed a nocturnal activity with diurnal overlaps no longer than 1 h. In 6 diurnal individuals first exposed to constant light and then to constant dim red light, the endogenous period was shortened from 24.6 +/- 0.1 to 24.0 +/- 0.1 h, respectively. The numbers of wheel revolutions per day and during the active period remained unchanged between the two lighting conditions. In response to different photoperiodic changes from 16:08 to 08:16 light-dark cycles, the phase angle of photic synchronization, estimated by the daily onset of wheel-running activity in 6 diurnal animals, showed marked changes, its timing occurring 2 h before and 0.5 h after the onset of light under short and long photoperiods, respectively. The numbers of wheel revolutions per 24 h and during the active period were modified similarly according to photoperiodic changes. Finally, in 5 diurnal animals exposed to a 12:12 light-dark cycle, the daily pattern of general locomotor activity, determined by telemetry, was not modified by wheel availability. The data indicate that A. ansorgei is an interesting experimental model to understand the regulation of the circadian timing system in day-active species.     

Interval timing in rats: tracking unsignaled changes in the fixed interval schedule requirement

The present experiment examined interval timing in rats under dynamic conditions. A session began with FI60 s intervals, changed to a FI20 s, FI30 s, or FI40 s schedule at an unpredictable point, and then returned to a FI60 s schedule after the rats received 1, 8, or 24 successive short FI intervals. Variations in the duration and number of shorter intervals occurred across sessions and conditions. We observed rapid control of wait time duration by the FI duration of the preceding interval (one-back tracking), and changes in wait time depended on the number and duration of the shorter intervals. Furthermore, we observed proportional and scalar timing effects in overall wait time duration. The results provide information about the relation between interval timing under dynamic and steady state conditions.     

The effects of 12-week progressive strength training on strength,functional capacity,metabolic biomarkers,and serum hormone concentrations in healthy older women: morning versus evening training

ABSTRACT

Previous findings suggest that performing strength training (ST) in the evening may provide greater benefit for young individuals. However, this may not be optimal for the older population. The purpose of this study was to compare the effects of a 12-week ST program performed in the morning vs. evening on strength, functional capacity, metabolic biomarker and basal hormone concentrations in older women. Thirty-one healthy older women (66 ± 4 years, 162 ± 4 cm, 75 ± 13 kg) completed the study. Participants trained in the morning (M) (07:30, n = 10), in the evening (E) (18:00, n = 10), or acted as a non-training control group (C) (n = 11). Both intervention groups performed whole-body strength training with 3 sets of 10–12 repetitions with 2–3 minutes rest between sets. All groups were measured before and after the 12-week period with; dynamic leg press and seated-row 6-repetition maximum (6-RM) and functional capacity tests (30-second chair stands and arm curl test, Timed Up and Go), as well as whole-body skeletal muscle mass (SMM) (kg) and fat mass (FM-kg, FM%) assessed by bioelectrical impedance (BIA). Basal blood samples (in the intervention groups only) taken before and after the intervention assessed low-density lipoprotein (LDL-C), high-density lipoprotein (HDL-C), blood glucose (GLU), triglycerides (TG), high-sensitive C-reactive protein (hsCRP) concentrations and total antioxidant status (TAS) after a 12 h fast. Hormone analysis included prolactin (PRL), progesterone (P) estradiol (ESTR), testosterone (T), follicle stimulating hormone (FSH), and luteinizing hormone (LH). While C showed no changes in any variable, both M and E significantly improved leg press (+ 46 ± 22% and + 21 ± 12%, respectively; p < 0.001) and seated-row (+ 48 ± 21% and + 42 ± 18%, respectively; p < 0.001) 6-RM, as well as all functional capacity outcomes (p < 0.01) due to training. M were the only group to increase muscle mass (+ 3 ± 2%, p < 0.01). Both M and E group significantly (p < 0.05) decreased GLU (–4 ± 6% and –8 ± 10%, respectively), whereas significantly greater decrease was observed in the E compared to the M group (p < 0.05). Only E group significantly decreased TG (–17 ± 25%, p < 0.01), whereas M group increased (+ 15%, p < 0.01). The difference in TG between the groups favored E compared to M group (p < 0.01). These results suggest that short-term “hypertrophic” ST alone mainly improves strength and functional capacity performance, but it influences metabolic and hormonal profile of healthy older women to a lesser extent. In this group of previously untrained older women, time-of-day did not have a major effect on outcome variables, but some evidence suggests that training in the morning may be more beneficial for muscle hypertrophy (i.e. only M significantly increased muscle mass and had larger effect size (M: g = 2 vs. E: g = 0.5).     

Neuromuscular efficiency of the triceps surae in induced and voluntary contractions: morning and evening evaluations

Variations in force and electromyographic (EMG) activities of skeletal muscles with the time-of-day have been previously described, but not for a postural muscle, submitted to daily postural and locomotor tasks. In this article, mechanical performances, EMGs, and the ratio between these parameters, i.e., the neuromuscular efficiency (NME), were measured on the triceps surae (TS) of eight subjects, two times each day, at 6:00 and 18:00 h. NME was evaluated under different experimental conditions (electrically induced contractions, reflex contractions, maximal and submaximal voluntary isometric contractions, and during a natural movement, a drop jump) to determine whether mechanisms, peripheral or central in origin, were responsible for the eventual changes in NME with time-of-day. To calculate NME in induced conditions (NMEind), a supramaximal electrical stimulus was applied to the tibial nerve, and the maximal M wave of TS (TS Mmax) and the amplitude of the twitch tension (PtMmax) in response to this electrical stimulation were quantified. TS Mmax was significantly lower in the evening (mean gain value -10.7 +/- 5.5%, p < 0.05), whereas PtMmax was not significantly modified. NMEind (PtMmax/TS Mmax) was significantly higher in the evening (mean gain of 17.6 +/- 5.8%, p < 0.05), and this increase was necessarily peripheral in origin. Secondly, maximal tendon taps were applied to the Achilles tendon in order to quantify at the two times-of-day the reflexes in response to a mechanical stimulus. The maximal reflex, TS Tmax/Mmax (%), the peak amplitude of the twitch tension associated to this tendon jerk (PtTmax), and the corresponding NME (NMEreflex = PtTmax/TS Tmax/Mmax) were not affected by time-of-day, indicating that reflex excitability did not present daytime variations when tested under these conditions. Voluntary isometric contractions were required under maximal (MVC) and submaximal (25% MVC) conditions, and the corresponding torques and TS EMG were measured. MVC was higher in the evening (mean gain: 8.6 +/- 2.7%, p < 0.05) and TS EMGmax (normalized with regard to TS Mmax) also increased in the evening but not significantly; thus, NMEMvc was not modified. At 25% of MVC, TS EMG was significantly higher in the evening (mean gain of 23 +/- 13.9%, p <0.05) and a trend for a lower NME25%MVC in the evening was observed, a result probably representative of a higher muscle fatigue state in the evening. Finally, to test the muscle capacities during a natural task, a NME index was calculated during a drop jump (DJ). The NMEDJ was defined as the ratio between jump height and mean amplitude of TS EMG (% of TS Mmax) between the drop and the jump. Both jump height and NMEDJ were significantly higher in the evening (mean gains of 10.9 +/- 4.5% and 15.7 +/- 7.4%, respectively, p <0.05). In conclusion, daytime changes in the efficiency of postural muscles seem to depend on both peripheral and central mechanisms. According to the experimental conditions, NME of the postural muscle could increase, remain constant, or even decrease in the evening, and this result may reflect reverse effects of better contractile capacities and higher fatigue state.     

Short and long-term effects of unguided internet-based cognitive behavioral therapy for chronic insomnia in morning and evening persons: a post-hoc analysis

ABSTRACT

A post-hoc analysis comparing morning and evening persons with insomnia on sleep and mental health characteristics was conducted in order to investigate whether an Internet-based cognitive behavioral therapy for insomnia (ICBTi) was effective both for morning and evening persons. Adult patients (N = 178, mean age = 44.8, 67% females) with insomnia were randomized to either ICBTi (N = 92; morning persons = 41; evening persons = 51) or a web-based patient education condition (N = 86; morning persons = 44; evening persons = 42). All patients were assessed with sleep diaries, the Insomnia Severity Index (ISI), the Bergen Insomnia Scale (BIS), the Dysfunctional Beliefs and Attitudes about Sleep Scale (DBAS-16), the Hospital Anxiety and Depression Scale (HADS) and the Chalder Fatigue Scale (CFQ). Patients were characterized as morning or evening persons based on a median split on the Horne-Östberg Morningness Eveningness Questionnaire. Short and long-term effects of treatment were examined with mixed-model repeated-measures analyses. Morning and evening persons did not differ in terms of age, gender or educational status. At baseline, morning persons had more wake time after sleep onset (d= 0.54, p < .001) and more early morning awakening (d= 0.38, p < .05) compared to evening persons, while evening persons reported longer sleep onset latency (d= 0.60, p < .001), more time in bed (d= 0.56, p < .001), longer total sleep time (d= 0.45, p < .01), more fatigue (d= 0.31, p < .05) and more dysfunctional beliefs and attitudes about sleep (d= 0.47, p < .01). Despite these differences at baseline, both morning and evening persons receiving ICBTi benefitted more across most measures compared to morning and evening persons who received patient education. For morning persons in the ICBTi group, ISI scores were reduced from 17.3 at baseline to 8.8 (d_pre-post = 2.48, p < .001) at post-assessment, and to 10.0 at 18-month follow up (d_pre-post18m = 2.13, p < .001). Comparable results were found for evening persons in the ICBTi group, with a reduction in ISI scores from 17.4 at baseline to 8.6 (d_pre-post = 2.24, p < .001) at post-assessment, and to 8.7 at 18-month follow up (d_pre-post18m = 2.19, p < .001). Similar results were found on the BIS, DBAS, HADS, CFQ and sleep diary data. Despite different insomnia symptomatology between the two groups, the current study suggests that ICBTi is effective across scores on the morningness-eveningness dimension. The study was pre-registered at: ClinicalTrials.gov Identifier: NCT02261272.     

Effect of morning school schedule on sleep and anthropometric variables in adolescents: a follow-up study

The aim of this study was to assess whether the shift from afternoon to morning classes reduces the duration of sleep and whether this reduction has any relation to body fat measurements. This is a follow-up study in which students (n = 379), 12.4 (SD(+/-)0.7) yrs old, were evaluated before and after the school schedule shift, with a 1-yr interval between the first and second data collections. Adolescents were divided into two groups: an afternoon-morning group (students who shifted from afternoon to morning classes) and an afternoon-afternoon group (students who remained in afternoon classes). The morning schedule of classes lasted from 07:30 and 12:00?h, and the afternoon schedule of classes lasted from 13:00 and 17:30?h. Self-reported bedtime, wake-up time, and time-in-bed were obtained. Body mass index, waist circumference, and body fat percentage were obtained by direct measures. The results showed a reduction of time-in-bed during weekdays for those students who changed to the morning session (p < .001). Analysis of covariance (ANCOVA) for repeated measures of anthropometric differences between afternoon-afternoon and afternoon-morning groups showed no effect of the school schedule change on weight gain. In conclusion, the time-in-bed reduction in the period analyzed cannot be considered to be a mediating factor to modifications in overweight anthropometric indicators.     

Relationship between cocaine-induced hepatotoxic neurobehavioral & biochemical changes in mice: the antidotal effects of buprenorphine

Cocaine (COCA)-induced neurobehavioral symptoms, which can be observed simultaneously with exacerbation in biochemical markers, were evaluated in mice, and compared with the changes observed in a representative hepatic failure model induced by thioacetamide (TAA). The effects of pretreatment with buprenorphine (BUP) (0.25, 0.5 or 1 mg/kg i.p.), a mixed opioid agonist-antagonist and an antidote against fatal COCA toxicity, were also examined. At 5 min after the COCA administration (65 mg/kg i.p.), the liver ATP levels were attenuated, and an exacerbation of the CNS-stimulating effects of COCA could be characteristically observed for hepatotoxicity-related neurobehavioral symptoms (changes in alertness, interest, body tension, head movement and walking). At 24 h, the ALT (alanine aminotransferase) activity was elevated, and hepatotoxic attenuation was observed for all of the scores on the neurobehavioral symptoms; this was almost identical to the symptoms observed in the TAA-treated group of mice. Recovery was observed by 72 h for all of the morbid changes. The hepatotoxic biochemical changes and the sum score for all five neurobehavioral symptoms were significantly ameliorated by low doses (0.25 and 0.5 mg/kg) of BUP, both at 5 min and 24 h.     

Effect of changes in feeding schedule on the diurnal rhythms and daily activity levels of intestinal brush border enzymes and transport systems

The activities of rat intestinal enzymes, sucrase, lactase, maltase, trehalase, γ-glutamyltransferase, leucylnaphthylamide-hydrolyzing activity, and the transport system for glucose follow diurnal rhythms on ad libitum and restricted feeding regimes. In response to 6 days of restricted feeding, food available between 1400 and 1800 Eastern Standard Time, all rhythms shifted in time and the daily levels of activities were changed. Alkaline phosphatase activity followed a diurnal rhythm only in restricted fed animals.In restricted fed rats several activity patterns were observed, some with short periods of maximum activity, 3 h or less, and some with plateaus of maximum activity, 5–9 h long. In respect to the time of day of the synchronizer, sucrase peaked before feeding, glucose transport peaked during feeding, alkaline phosphatase peaked after feeding, and the other enzymes had higher levels of activity before, during and after feeding. The effect of restricted feeding on the daily activity levels were: a decrease in leucylnaphthylamide-hydrolyzing activity, no change in alkaline phosphatase, and increases in the others.These enzyme and transport systems exhibit a large amount of individual regulation or control as reflected by the lack of a uniform activity pattern and response to the synchronizer, and the variation in direction and magnitude of the adaptations to restricted feeding.     

Effect of changes in feeding schedule on the diurnal rhythms and daily activity levels of intestinal brush border enzymes and transport systems.

The activities of rat intestinal enzymes, sucrase, lactase, maltase, trehalase, gamma-glutamyltransferase, leucylnaphthylamide-hydrolyzing activity, and the transport system for glucose follow diurnal rhythms on ad libitum and restricted feeding regimes. In response to 6 days of restricted feeding, food available between 1400 and 1800 Eastern Standard Time, all rhythms shifted in time and the daily levels of activities were changed. Alkaline phosphatase activity followed a diurnal rhythm only in restricted fed animals. In restricted fed rats several activity patterns were observed, some with short periods of maximum activity, 3 h or less, and some with plateaus of maximum activity, 5-9 h long. In respect to the time of day of the synchronizer, sucrase peaked before feeding, glucose transport peaked during feeding, alkaline phosphatase peaked after feeding, and the other enzymes had higher levels of activity before, during and after feeding. The effect of restricted feeding on the daily activity levels were: a decrease in leucylnaphthylamide-hydrolyzing activity, no change in alkaline phosphatase, and increases in the others. These enzyme and transport systems exhibit a large amount of individual regulation or control as reflected by the lack of a uniform activity pattern and response to the synchronizer, and the variation in direction and magnitude of the adaptations to restricted feeding.     

Effect of cortisol on estradiol secretion and its reception in the morning and evening hours in 30-day-old female rats

Cortisol administration (250 micrograms) to 5-day-old female rats was studied for its effect on the diurnal (morning-evening) rhythm of the estradiol secretion and reception on the 30th day of life. This stimulus had no influence on the estradiol level in the morning time. In the evening the estrogen concentration in the control group decreased while in the cortisol-treated group there were no changes. Disturbance of the circadian periodicity in the serum estradiol concentration in cortisol-treated animals was not induced by changes in the secretory ability of adrenals and ovaries, which was estimated by measurement of the estradiol production by glands in vitro. This disturbance was not a result of changes in hormone reception in uterine cytosol. The increased estradiol level in cortisol-treated rats in the evening is in good agreement with effects caused by neonatal glucocorticoid treatment in the reproductive system.     

Comparison of the effects of zolpidem and zopiclone on nocturnal sleep and sleep latency in the morning: a cross-over study in healthy young volunteers

Zolpidem (ZOL) and zopiclone (ZPC) are non-benzodiazepine hypnotics, with unique effects on sleep architecture compared with conventional benzodiazepines. The two compounds have different profiles in action to two major subtypes of the GABA-A receptors, therefore different effects on sleep structure may be expected. In the present study, the effects of ZOL (10mg) and ZPC (7.5mg) were compared in nine healthy young male subjects during nine-night sessions, employing a crossover design. Time courses during the sessions were significantly different between the compounds in the ratio (%) of S2 and S1. Compared to the baseline, an increase of S2 and a decrease of S1 and SR were caused by ZPC, not by ZOL. SWS was increased by both ZPC and ZOL. Significant changes by ZOL were found during the first 150-min, while changes by ZPC were mostly observed during the second 150-min. This might be related to their half-lives. ZOL did not affect sleep latency in the morning, while ZPC caused a significant decrease. Subjective sleepiness, however, was not increased in the ZPC or ZOL mornings. It was speculated that difference in the action to the GABA-A receptor subtypes might be related to the differences in the effects on the sleep architecture between the compounds.     

Rate effects on timing, key velocity, and finger kinematics in piano performance

We examined the effect of rate on finger kinematics in goal-directed actions of pianists. In addition, we evaluated whether movement kinematics can be treated as an indicator of personal identity. Pianists' finger movements were recorded with a motion capture system while they performed melodies from memory at different rates. Pianists' peak finger heights above the keys preceding keystrokes increased as tempo increased, and were attained about one tone before keypress. These rate effects were not simply due to a strategy to increase key velocity (associated with tone intensity) of the corresponding keystroke. Greater finger heights may compensate via greater tactile feedback for a speed-accuracy tradeoff that underlies the tendency toward larger temporal variability at faster tempi. This would allow pianists to maintain high temporal accuracy when playing at fast rates. In addition, finger velocity and accelerations as pianists' fingers approached keys were sufficiently unique to allow pianists' identification with a neural-network classifier. Classification success was higher in pianists with more extensive musical training. Pianists' movement "signatures" may reflect unique goal-directed movement kinematic patterns, leading to individualistic sound.     

The effects of walking speed on obstacle crossing in healthy young and healthy older adults

The effects of walking speed and age on the peak external moments generated about the joints of the trailing limb during stance just prior to stepping over an obstacle and on the kinematics of the trailing limb when crossing the obstacle were investigated in 10 healthy young adults (YA) and 10 healthy older adults (OA). The peak hip and knee adduction moments in OA were 21-43% greater than those in YA (p相似文献   

Damage-induced changes in woody plants and their effects on insect herbivore performance: a meta-analysis

We conducted a meta‐analysis of 68 studies published between 1982 and 2000 in which the responses of woody plants to natural or simulated herbivore damage and/or insect herbivore performance on control and damaged plants were measured. Cumulative meta‐analyses revealed dramatic temporal changes in the magnitude and direction of the plant and herbivore responses reported during the last two decades. Studies conducted in the 1980s reported increase in phenolic concentrations, reduction in nutrient concentrations and negative effect on herbivore performance, consistently with the idea of induced resistance. In contrast, in the early 1990s when the idea that some types of plant damage may result in induced susceptibility was generally accepted, studies reported non‐significant results or induced susceptibility, and smaller effects on herbivores. The above changes may reflect paradigm shifts in the theory of induced defenses and/or the differences between study systems used in the early and the more recent studies. Overall, plant growth and carbohydrate concentrations were reduced in damaged plants despite enhanced photosynthetic rates. Damage increased the concentrations of carbon and phenolics, while terpene concentrations tended to decrease after damage; changes in nutrient concentrations after damage varied according to nutrient mobility, inherent plant growth rate, ontogenetic stage and plant type (deciduous/evergreen). Early season damage caused more pronounced changes in plants than late season damage, which is in accordance with the assumption that vigorously growing foliage has a greater capacity to respond to damage. Insect growth rate and female pupal weight decreased on previously damaged plants, while herbivore survival, consumption and male pupal weight were not significantly affected. The magnitude and direction of herbivore responses depended on the type of plant, the type of damage, the time interval between the damage and insect feeding (rapid/delayed induced resistance), and the timing of the damage.     

Time course and dose-response effects of orally administered delta-9-THC on interval schedule performance of the rat

Rats that had been trained on fixed or variable interval schedules of food reinforcement were given oral administrations of 4, 8, 16, and 32 mg/kg of delta-9-tetrahydrocannabinol at various times prior to experimental sessions. The two lower doses either had no effect or increased response rates up to 8 hours post-administration. The two higher doses suppressed responding, with a maximum effect about 24 hours post-administration. Responding recovered to baseline levels about 30 hours after drug administration.     

Responses of plasma adrenocorticotropin and cortisol to intravenous injection of synthetic ovine corticotropin releasing factor in the morning and early evening in normal human subjects

This study was designed to compare the responsiveness of adrenocorticotropin (ACTH) and cortisol secretion to corticotropin-releasing factor (CRF) in the morning and early evening in normal human subjects. Synthetic ovine CRF (1.0 micrograms/kg) or normal saline, was administered as an i.v. bolus injection to six normal males at 900 h and 1700 h. Blood samples were obtained before and 15, 30, 60, 90 and 120 min after CRF or saline injection. Significant increases in plasma ACTH and cortisol levels were observed in all subjects at the both time of testing after CRF injection. The net increments in the areas under the concentration curve (areas in the CRF experiment minus those in the saline control experiment) were not statistically different for both ACTH (mean +/- SEM: 41.0 +/- 10.6 pg/ml h in the morning: 51.1 +/- 8.9 pg/ml h in the evening) and cortisol (mean +/- SEM: 28.5 +/- 5.0 micrograms/dl h in the morning; 36.2 +/- 4.0 micrograms/dl h in the evening). Also no significant difference was observed in net increment, peak level and the ratio of peak level to the basal level of ACTH and cortisol after CRF injection. There were no appreciable changes in plasma concentrations of growth hormone, thyroid-stimulating hormone or prolactin, although slight but statistically significant rises in plasma levels of luteinizing hormone and follicle-stimulating hormone were observed. These results suggest that there is no significant difference in responsiveness of the pituitary-adrenal axis to CRF in the morning (900 h) and early evening (1700 h), and thus the time of day will not necessarily have to be considered when CRF is used between these times in a clinical test to evaluate pituitary ACTH reserve.     

Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring

Prior work shows western US forest wildfire activity increased abruptly in the mid-1980s. Large forest wildfires and areas burned in them have continued to increase over recent decades, with most of the increase in lightning-ignited fires. Northern US Rockies forests dominated early increases in wildfire activity, and still contributed 50% of the increase in large fires over the last decade. However, the percentage growth in wildfire activity in Pacific northwestern and southwestern US forests has rapidly increased over the last two decades. Wildfire numbers and burned area are also increasing in non-forest vegetation types. Wildfire activity appears strongly associated with warming and earlier spring snowmelt. Analysis of the drivers of forest wildfire sensitivity to changes in the timing of spring demonstrates that forests at elevations where the historical mean snow-free season ranged between two and four months, with relatively high cumulative warm-season actual evapotranspiration, have been most affected. Increases in large wildfires associated with earlier spring snowmelt scale exponentially with changes in moisture deficit, and moisture deficit changes can explain most of the spatial variability in forest wildfire regime response to the timing of spring.This article is part of the themed issue ‘The interaction of fire and mankind’.