The purpose of this study was to test the effect of subconcussive head impacts on acute changes in plasma S100B. In this randomized controlled trial, 79 healthy adult soccer players were randomly assigned to either the heading (n = 41) or kicking-control groups (n = 38). The heading group executed 10 headers with soccer balls projected at a speed of 25 mph, whereas the kicking-control group performed 10 kicks. Plasma samples were obtained at pre-, 0h post-, 2h post- and 24h post-intervention and measured for S100B. The primary hypothesis was that there would be a significant group difference (group-by-time interaction) in plasma S100B at 2h post-intervention. Secondary hypotheses included (1) no significant group differences in plasma S100B concentrations at 0h post- and 24h post-intervention; (2) a significant within-group increase in S100B concentrations in the heading group at 2h post-intervention compared to pre-intervention; and (3) no significant within-group changes in plasma S100B in the kicking-control group. Data from 68 subjects were available for analysis (heading n = 37, kicking n = 31). There were no differences in S100B concentrations between heading and kicking groups over time, as evidenced by nonsignificant group-by-time interaction at 2h post-intervention (B = 2.20, 95%CI [-22.22, 26.63], p = 0.86) and at all the other time points (0h post: B = -11.05, 95%CI [-35.37, 13.28], p = 0.38; 24h post: B = 16.11, 95%CI [-8.29, 40.51], p = 0.20). Part of the secondary outcome, the heading group showed elevation in plasma S100B concentrations at 24h post-intervention compared to pre-heading baseline (B = 19.57, 95%CI [3.13, 36.02], p = 0.02), whereas all other within-group comparisons in both remained nonsignificant. The data suggest that 10 bouts of acute controlled soccer headings do not elevate S100B concentrations up to 24-hour post-heading. Further dose-response studies with longer follow-up time points may help determine thresholds of acute soccer heading exposure that are related to astrocyte activation. The protocol was registered under ClinicalTrials.gov ( NCT03488381 ; retrospectively registered.).

Objective: To examine changes in plasma levels of CCL11, CCL2, and IL-10 after 10 controlled soccer headers. Setting: Laboratory setting. Participants: Thirty-nine healthy soccer players with at least 3 years of soccer heading experience, between 18 and 26 years old, and enrolled at a large public university. Design: In this randomized clinical trial using a soccer heading model, participants were randomized into the heading (n = 22) or kicking-control (n = 17) groups to perform 10 headers or kicks. Main Measures: Plasma levels of CCL11, CCL2, and IL-10 at preintervention and 0, 2, and 24 hours postintervention. Results: Mixed-effects regression models did not reveal any significant group differences in changes of plasma CCL11, CCL2, or IL-10 levels from preintervention. Within the heading group, there was a statistically significant time by years of heading experience interaction with 2.0-pg/mL increase in plasma CCL11 each year of prior experience at 24 hours postintervention (P = .001). Conclusion: Findings from this study suggest that 10 soccer headers do not provoke an acute inflammatory response. However, the acute CCL11 response may be influenced by prior exposure to soccer headers, providing a precedent for future field studies that prospectively track head impact exposure and changes in CCL11.

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Cannabis is an increasingly popular recreational drug among college students. Prior investigations have shown that acute cannabis use alters heart rate variability via increased sympathetic activation. However, the effects of chronic cannabis use on heart rate variability (HRV) have not been reported. PURPOSE We tested the hypothesis that HRV would be lower in chronic cannabis users (THC) compared to non‐users (CON). METHODS Eleven cannabis users (age: 21±2 y, 2 females) and six controls (age: 20±2 y; 4 females) completed one study visit. Participants in the THC group self‐reported using cannabis at least once per week for the past year or more. Participants in the CON reported to not use for 6 months prior to enrollment. Participants were instructed to abstain from alcohol for 24 h and cannabis for 72 h prior to the study visit. After 10 minutes of supine rest, heart rate (5‐lead electrocardiogram) was continuously recorded at 1 kHz for 5 minutes of supine rest while participants breathed spontaneously. HRV was assessed using linear analysis via Fast Fourier transformation and non‐linear analysis via Poincare plots. The root mean square of successive differences (RMSSD), percent of R‐R intervals that differ by more than 50 ms (pRR50), and the standard deviation of R‐R intervals (SDRR) were calculated to assess HRV in the time‐domain. Fast Fourier transformation was used to assess HRV in the frequency domain (low‐frequency (LF) and high‐frequency (HF) power). Non‐linear HRV analysis was performed using Poincare plots to calculate standard deviation 1 (SD1) and 2 (SD2). We used one‐tailed unpaired t‐tests to determine if the main outcome variables were different between groups. Values are reported as mean ± SD. RESULTS RRI was lower in THC (THC: 917±109 vs. CON: 1018±141 ms; P=0.06). RMSSD was lower in THC (THC: 57±21 vs. CON: 74±24 ms; P=0.07). There was no difference between groups for pRR50 (THC: 36±20 vs. CON: 47±21 %; P=0.12) or SDRR (THC: 68±16 vs. CON: 78±24 ms; P=0.15). LF power was not different between groups (THC: 1105±850 vs. CON: 1321±852 ms2; P=0.31), but HF power was lower in THC (THC: 1353±925 vs. CON: 2256±1195 ms2; P=0.05). SD1 was lower in THC (THC: 40±15 vs. CON: 53±17 ms; P=0.07). SD2 was not different between groups (THC: 86±19 vs. CON: 96±33 ms; P=0.23). CONCLUSION These preliminary data indicate that college‐aged adults who regularly use cannabis have lower heart rate variability than their non‐cannabis user counterparts. Based on linear and non‐linear analyses, it appears that cannabis users have altered cardiac vagal activity at rest. However, more research is warranted to determine if cannabis use alters autonomic function and reactivity.

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