An Acute Bout of Endurance Exercise Does Not Prevent the Inhibitory Effect of Caffeine on Glucose Tolerance the following Morning

Caffeine reduces glucose tolerance, whereas exercise training improves glucose homeostasis. The aim of the present study was to investigate the effect of caffeine on glucose tolerance the morning after an acute bout of aerobic exercise. Methods: The study had a 2 × 2 factorial design. Oral glucose tolerance tests (OGTT) were performed after overnight fasting with/without caffeine and with/without exercise the evening before. Eight healthy young active males were included (Age 25.5 ± 1.5 years; 83.9 ± 9.0 kg; VO_2max: 54.3 ± 7.0 mL·kg^-1·min^-1). The exercise session consisted of 30 min cycling at 71% of VO_2max followed by four 5 min intervals at 84% with 3 min of cycling at 40% of VO_2max between intervals. The exercise was performed at 17:00 h. Energy expenditure at each session was ~976 kcal. Lactate increased to ~8 mM during the exercise sessions. Participants arrived at the laboratory the following morning at 7.00 AM after an overnight fast. Resting blood samples were taken before blood pressure and heart rate variability (HRV) were measured. Caffeine (3 mg/kg bodyweight) or placebo (similar taste/flavor) was ingested, and blood samples, blood pressure and HRV were measured after 30 min. Next, the OGTTs were initiated (75 g glucose dissolved in 3 dL water) and blood was sampled. Blood pressure and HRV were measured during the OGTT. Caffeine increased the area under curve (AUC) for glucose independently of whether exercise was done the evening before (p = 0.03; Two-way ANOVA; Interaction: p = 0.835). Caffeine did not significantly increase AUC for C-peptides compared to placebo (p = 0.096), and C-peptide response was not influenced by exercise. The acute bout of exercise did not significantly improve glucose tolerance the following morning. Diastolic blood pressure during the OGTT was slightly higher after intake of caffeine, independent of whether exercise was performed the evening before or not. Neither caffeine nor exercise the evening before significantly influenced HRV. In conclusion, caffeine reduced glucose tolerance independently of whether endurance exercise was performed the evening before. The low dose of caffeine did not influence heart rate variability but increased diastolic blood pressure slightly.

Training Load Measures and Biomarker Responses during a 7-Day Training Camp in Young Cyclists-A Pilot Study

Background and Objectives: During intense training periods, there is a high need to monitor the external and especially the internal training load in order to fine-tune the training process and to avoid overreaching or overtraining. However, data on stress reactions, especially of biomarkers, to high training loads in children and youth are rare. Therefore, in this study, we aimed to investigate the training load of youth athletes during a training camp using a multilevel approach. Materials and Methods: Six trained youth male cyclists performed a 7-day preseason training camp. To investigate the internal training load, every morning, minimally invasive “point-of-care testing” (POCT) devices were used to analyze the following biomarkers: creatine kinase (CK), blood urea nitrogen (BUN), albumin (Alb), bilirubin (Bil), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total protein (TP). Additionally, data of training load measures (HR: heart rate, RPE: rating of perceived exertion, sRPE: session-RPE, TRIMP: training impulse, intensity (RPE:HR), and load (sRPE:TRIMP) ratios), self-perception (person’s perceived physical state, questionnaires on muscle soreness, and sleep quality), and measures of the autonomic nervous system (resting heart rate, heart rate variability) were collected. Two days before and after the training camp, subjects performed performance tests (Graded Exercise Test, Wingate Anaerobic Test, Counter Movement Jump). Results: Primarily, the biomarkers CK, BUN, and Alb, as well as the self-perception showed moderate to large load-dependent reactions during the 7-day training camp. The biomarkers returned to baseline values two days after the last training session. Power output at lactate threshold showed a small increase, and no changes were found for other performance parameters. Conclusions: The study suggests that a multilevel approach is suitable to quantify the internal training load and that different parameters can be used to control the training process. The biomarkers CK, BUN, and Alb are suitable for objectively quantifying the internal training load. The self-perception provides additional subjective information about the internal training load.

A strength-oriented exercise session required more recovery time than a power-oriented exercise session with equal work

The present randomized cross-over controlled study aimed to compare the rate of recovery from a strength-oriented exercise session vs. a power-oriented session with equal work. Sixteen strength-trained individuals conducted one strength-oriented session (five repetitions maximum (RM)) and one power-oriented session (50% of 5RM) in randomized order. Squat jump (SJ), countermovement jump (CMJ), 20-m sprint, and squat and bench press peak power and estimated 1RMs were combined with measures of rate of perceived exertion (RPE) and perceived recovery status (PRS), before, immediately after and 24 and 48 h after exercise. Both sessions induced trivial to moderate performance decrements in all variables. Small reductions in CMJ height were observed immediately after both the strength-oriented session (7 ± 6%) and power-oriented session (5 ± 5%). Between 24 and 48 h after both sessions CMJ and SJ heights and 20 m sprint were back to baseline. However, in contrast to the power-oriented session, recovery was not complete 48 h after the strength-oriented session, as indicated by greater impairments in CMJ eccentric and concentric peak forces, SJ rate of force development (RFD) and squat peak power. In agreement with the objective performance measurements, RPE and PRS ratings demonstrated that the strength-oriented session was experienced more strenuous than the power-oriented session. However, these subjective measurements agreed poorly with performance measurements at the individual level. In conclusion, we observed a larger degree of neuromuscular impairment and longer recovery times after a strength-oriented session than after a power-oriented session with equal total work, measured by both objective and subjective assessments. Nonetheless, most differences were small or trivial after either session. It appears necessary to combine several tests and within-test analyses (e.g., CMJ height, power and force) to reveal such differences. Objective and subjective assessments of fatigue and recovery cannot be used interchangeably; rather they should be combined to give a meaningful status for an individual in the days after a resistance exercise session.

Optimisation of assessment of maximal rate of heart rate increase for tracking training-induced changes in endurance exercise performance

The maximal rate of heart rate (HR) increase (rHRI), a marker of HR acceleration during transition from rest to submaximal exercise, correlates with exercise performance. In this cohort study, whether rHRI tracked performance better when evaluated over shorter time-periods which include a greater proportion of HR acceleration and less steady-state HR was evaluated. rHRI and five-km treadmill running time-trial performance (5TTT) were assessed in 15 runners following one week of light training (LT), two weeks of heavy training (HT) and 10-day taper (T). rHRI was the first derivative maximum of a sigmoidal curve fit to one, two, three and four minutes of R-R data during transition from rest to running at 8 km/h (rHRI_8 km/h), 10.5 km/h_, 13 km/h and transition from 8 to 13 km/h (rHRI_8–13km/h). 5TTT time increased from LT to HT (effect size [ES] 1.0, p < 0.001) then decreased from HT to T (ES −1.7, p < 0.001). 5TTT time was inversely related to rHRI_8 km/h assessed over two (B = −5.54, p = 0.04) three (B = −5.34, p = 0.04) and four (B = −5.37, p = 0.04) minutes, and rHRI_8–13km/h over one (B = −11.62, p = 0.006) and three (B = −11.44, p = 0.03) minutes. 5TTT correlated most consistently with rHRI_8 km/h. rHRI_8 km/h assessed over two to four minutes may be suitable for evaluating athlete responses to training.

Maximal Heart Rate for Swimmers

The main purpose of this study was to identify whether a different protocol to achieve maximal heart rate should be used in sprinters when compared to middle-distance swimmers. As incorporating running training into swim training is gaining increased popularity, a secondary aim was to determine the difference in maximal heart rate between front crawl swimming and running among elite swimmers. Twelve elite swimmers (4 female and 8 male, 7 sprinters and 5 middle-distance, age 18.8 years and body mass index 22.9 kg/m²) swam three different maximal heart rate protocols using a 50 m, 100 m and 200 m step-test protocol followed by a maximal heart rate test in running. There were no differences in maximal heart rate between sprinters and middle-distance swimmers in each of the swimming protocols or between land and water (all p ≥ 0.05). There were no significant differences in maximal heart rate beats-per-minute (bpm) between the 200 m (mean ± SD; 192.0 ± 6.9 bpm), 100 m (190.8 ± 8.3 bpm) or 50 m protocol (191.9 ± 8.4 bpm). Maximal heart rate was 6.7 ± 5.3 bpm lower for swimming compared to running (199.9 ± 8.9 bpm for running; p = 0.015). We conclude that all reported step-test protocols were suitable for achieving maximal heart rate during front crawl swimming and suggest that no separate protocol is needed for swimmers specialized on sprint or middle-distance. Further, we suggest conducting sport-specific maximal heart rate tests for different sports that are targeted to improve the aerobic capacity among the elite swimmers of today.

Mesocycles with Different Training Intensity Distribution in Recreational Runners

PURPOSE

The aim was to compare mesocycles with progressively increasing workloads and varied training intensity distribution (TID), that is, high-intensity (HIGH, > 4 mmol·L blood lactate), low-intensity (LOW, < 2 mmol·L blood lactate) or a combination of HIGH and LOW (referred to as "polarized" [POL]) on 5000-m running time and key components of endurance performance in recreational runners.

METHODS

Forty-two runners (peak oxygen uptake (V˙O2peak): 45.2 ± 5.8 mL·min·kg) were systematically parallelized to one of three groups performing a 4-wk mesocycle with equal TID (two to four training sessions) followed by a 3-wk mesocycle with increased weekly training impulse (i.e., 50% increase compared to the first 4-wk mesocycle) of either HIGH, LOW, or POL and 1 wk tapering. V˙O2peak, velocity at lactate threshold and running economy were assessed at baseline (T0), after 4 wk (T1), 7 wk (T2), and 8 wk (T3).

RESULTS

The 5000-m time decreased in all groups from T0 to T2 and T3. V˙O2peak increased from T0 to T2 and T3 (P < 0.03) with HIGH and from T0 to T2 (P = 0.02) in LOW and from T0 to T3 (P = 0.006) with POL. Running economy improved only from T1 to T3 and from T2 to T3 (P < 0.04) with LOW. An individual mean response analysis indicated a high number of responders (n = 13 of 16) in LOW, with less in HIGH (n = 6/13) and POL (n = 8/16).

CONCLUSIONS

On a group level, HIGH, LOW, and POL improve 5000-m time and V˙O2peak. Changes in running economy occurred only with LOW. Based on the individual response of recreational runners the relative risk of nonresponding is greater with HIGH and POL compared with LOW.

Evidence of reduced parasympathetic autonomic regulation in inflammatory joint disease: A meta-analyses study

BACKGROUND

Rheumatoid arthritis (RA) and spondyloarthritis (SpA) are inflammatory joint disorders (IJD) with increased risk of cardiovascular disease (CVD). Autonomic dysfunction (AD) is a risk factor for CVD, and parasympathetic AD is linked to key features of IJD such as inflammation, physical inactivity and pain. Heart-rate variability (HRV) is a marker of cardiac AD. The study objective was to compare parasympathetic cardiac AD, measured by HRV, between patients with IJD and healthy controls, using meta-analysis methodology, and to examine the impact of inflammation, physical inactivity and pain on HRV in IJD.

METHODS

Medline, Embase and Amed were searched. Inclusion criteria were adult case-control studies published in English or a Scandinavian language, presenting HRV data in IJD. Two measures of HRV and 3 from the Ewing protocol were selected: square root of mean squared difference of successive R-R intervals (RMSSD), high frequency (HF), Ewing protocol; standing (E-S), breathing (E-B) and Valsalva (E-V). Patients with RA, SpA and healthy controls were compared separately using random-effects meta-analyses of standardized mean differences (SMD).

RESULTS

In all, 35 papers were eligible for inclusion. For RMSSD the pooled SMD (95% CI) RA vs. controls was -0.90 (-1.35 to -0.44), for SpA vs. controls; -0.34 (-0.73 to 0.06). For HF pooled SMD RA vs. controls was -0.78 (-0.99 to -0.57), for SpA vs. controls; -0.04 (-0.22 to 0.13). All Ewing parameters were significantly lower in cases, except for E-V which was comparable between cases and controls in patients with RA.

CONCLUSION

Patients with IJD have cardiac parasympathetic AD which is related to inflammation.

Reliability and validity of time domain heart rate variability during daily routine activities – an alternative to the morning orthostatic test?

Study aim: To determine the reliability and validity of a time domain heart rate variability (HRV) index during free-living physical activity (FLPA).

Material and methods: Eight white-collar workers participated in this study. RR intervals (time between consecutive R-peaks of the PQRS complex) were recorded using the Polar V800 heart rate (HR) monitor upon awakening and at work on 16 different days. A total of 127 cycles of sitting periods followed by walking breaks were included for consecutive pairwise analysis for reliability. The HR values from the orthostatic test (OT) were compared with the corresponding values at work.

Results: The HR values showed high levels of repeatability [the coefficient of variation (CV) during sitting and walking at work was 4.71 and 3.99%, respectively, with a typical error (TE) of 3.73 (3.34-4.25) and 3.65 (3.31-4.09)], but they did not correlate with the corresponding OT HR upon awakening (r = 0.28 for supine vs. sitting and r = 0.05 for standing vs. walking, p > 0.05). The root-mean-square difference of successive normal RR (RMSSD) was revealed not to be repeatable [CV values during sitting and walking were 19.99 and 29.05%, respectively, with a TE of 7.9 (7.15-8.85) and 9.43 (8.53-10.57)].

Conclusions: Analyzing RMSSD from daily routine activities was not reliable, and therefore validity cannot be assumed. RMSSD should therefore be calculated from RR intervals recorded in standardized conditions, such as during the OT upon awakening.

Acute Effects of Caffeine on Heart Rate Variability, Blood Pressure and Tidal Volume in Paraplegic and Tetraplegic Compared to Able-Bodied Individuals: A Randomized, Blinded Trial

Caffeine increases sympathetic nerve activity in healthy individuals. Such modulation of nervous system activity can be tracked by assessing the heart rate variability. This study aimed to investigate the influence of caffeine on time- and frequency-domain heart rate variability parameters, blood pressure and tidal volume in paraplegic and tetraplegic compared to able-bodied participants. Heart rate variability was measured in supine and sitting position pre and post ingestion of either placebo or 6 mg caffeine in 12 able-bodied, 9 paraplegic and 7 tetraplegic participants in a placebo-controlled, randomized and double-blind study design. Metronomic breathing was applied (0.25 Hz) and tidal volume was recorded during heart rate variability assessment. Blood pressure, plasma caffeine and epinephrine concentrations were analyzed pre and post ingestion. Most parameters of heart rate variability did not significantly change post caffeine ingestion compared to placebo. Tidal volume significantly increased post caffeine ingestion in able-bodied (p = 0.021) and paraplegic (p = 0.036) but not in tetraplegic participants (p = 0.34). Systolic and diastolic blood pressure increased significantly post caffeine in able-bodied (systolic: p = 0.003; diastolic: p = 0.021) and tetraplegic (systolic: p = 0.043; diastolic: p = 0.042) but not in paraplegic participants (systolic: p = 0.09; diastolic: p = 0.33). Plasma caffeine concentrations were significantly increased post caffeine ingestion in all three groups of participants (p<0.05). Plasma epinephrine concentrations increased significantly in able-bodied (p = 0.002) and paraplegic (p = 0.032) but not in tetraplegic participants (p = 0.63). The influence of caffeine on the autonomic nervous system seems to depend on the level of lesion and the extent of the impairment. Therefore, tetraplegic participants may be less influenced by caffeine ingestion.