Christopher Kirk

Dr. Christopher Kirk

orcid

Research Focus & Metrics

Academic Career Length

12Years (2015-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

View All Publications
3 January 2020 in Journal of Strength & Conditioning Research
Verified
Journal Article
Closed access
BVBreno B. Vasconcelos
Breno B. Vasconcelos
GPGabriel V. Protzen
Gabriel V. Protzen
LGLeony M. Galliano
Leony M. Galliano
CKChristopher Kirk
Christopher Kirk
FVFabrício Boscolo Del Vecchio
Fabrício Boscolo Del Vecchio
Vasconcelos, BB, Protzen, GV, Galliano, LM, Kirk, C, and Del Vecchio, FB. Effects of high-intensity interval training in combat sports: A systematic review with meta-analysis. J Strength Cond Res 34(3): 888–900, 2020—Combat sports (CS) are intermittent by nature and high-intensity interval training (HIIT) has been used as a tool to maintain and improve physical fitness among CS athletes. The aim of this study was to perform a systematic review and meta-analysis about chronic effects of HIIT in CS athletes. An electronic search was performed in PubMed, Science Direct, and Google Scholar using the following Boolean criteria: (“CS” OR “martial arts” OR “judo” OR “taekwondo” OR “jiu jitsu” OR “boxing” OR “karate” OR “wrestling” OR “wushu” OR “kung fu”) AND (“HIIT” OR “intermittent exercise” OR “sprint interval training” OR “repeated sprint training [RST]”). To be included, the studies needed to be original, involve CS athletes, present HIIT intervention protocol (HIIT, sprint interval training [SIT] or RST), and analyze chronic physiological outcomes. From 2,211 identified studies, after screening and eligibility evaluation, 12 studies were included in this review with meta-analysis. Aerobic (aerobic capacity, heart rate, and maximum oxygen uptake), anaerobic (peak and mean power in single and successive Wingate tests, and blood lactate concentration), and anthropometric outcomes (body mass and body fat percentage) were evaluated. Data of 255 subjects from 12 studies were assessed. Regarding methodological quality, 7 studies obtained 9–10/12 on the TESTEX scale. For the interventions, 5 studies used HIIT, 4 studies used RST protocols, one used SIT protocols, and one used an intermittent protocol that could not be classified. Relating to aerobic power, was found an increase in V̇O2max, with a mean difference (MD) of 2.83 ml·kg−1·min−1 (CI 95% = 0.40–5.25; p < 0.001) for striking and 2.36 ml·kg−1·min−1 (CI 95% = 1.05–3.66; p < 0.001) for grappling athletes. No differences on anaerobic peak power for striking (MD = 0.67 W; CI 95% = −0.43 to 1.77; p = 0.23) were found, and a statistical improvement for grappling athletes, (MD = 0.51 W; CI 95% = 0.03–0.98; p = 0.04) was found. Seven studies analyzed anthropometric variables, with differences for body mass in striking (MD = −0.93 kg; CI 95% = −1.68 to −0.19; p = 0.01) and no differences for grappling (MD = −0.09 kg; CI 95% = −2.80 to 2.62; p = 0.95). Differences in body fat percentage in striking (MD = 0.50%; CI 95% = 0.30–0.70; p < 0.001) and no differences in grappling (MD = −0.87%; CI 95% = −1.77 to 0.03; p = 0.06) were found. It was concluded that HIIT positively influences maximum oxygen uptake and anaerobic power in combat sport athletes, with a minor impact on body composition.

10 May 2021 in PLOS ONE
Verified
Journal Article
Open access
PDF file
CKChristopher Kirk
Christopher Kirk
CLCarl Langan-Evans
Carl Langan-Evans
DCDavid R. Clark
David R. Clark
JMJames P. Morton
James P. Morton
The aim of this study was to quantify typical training load and periodisation practices of MMA athletes. MMA competitors (n = 14; age = 22.4 ± 4.4 years; body mass = 71.3 ± 7.7 kg; stature = 171 ±9.9 cm) were observed during training for 8 consecutive weeks without intervention. Seven athletes were training for competitive bouts whilst the remaining 7 were not. Daily training duration, intensity (RPE), load (sRPE and segRPE), fatigue (short questionnaire of fatigue) and body region soreness (CR10 scale) were recorded. Using Bayesian analyses (BF10≥3), data demonstrate that training duration (weekly mean range = 3.9–5.3 hours), sRPE (weekly mean range = 1,287–1,791 AU), strain (weekly mean range = 1,143–1,819 AU), monotony (weekly mean range = 0.63–0.83 AU), fatigue (weekly mean range = 16–20 AU) and soreness did not change within or between weeks. Between weeks monotony (2.3 ± 0.7 AU) supported little variance in weekly training load. There were no differences in any variable between participants who competed and those who did not with the except of the final week before the bout, where an abrupt step taper occurred leading to no between group differences in fatigue. Training intensity distribution corresponding to high, moderate and low was 20, 33 and 47%, respectively. Striking drills accounted for the largest portion of weekly training time (20–32%), with MMA sparring the least (2–7%). Only striking sparring and wrestling sparring displayed statistical weekly differences in duration or load. Athletes reported MMA sparring and wrestling sparring as high intensity (RPE≥7), BJJ sparring, striking sparring and wrestling drills as moderate intensity (RPE 5–6), and striking drills and BJJ drills as low intensity (RPE≤4). We conclude that periodisation of training load was largely absent in this cohort of MMA athletes, as is the case within and between weekly microcycles.

21 March 2024 in Scandinavian Journal of Medicine & Science in Sports
Verified
Journal Article
Open access
Tommy LundbergTommy Lundberg
Tommy Lundberg
RTRoss Tucker
Ross Tucker
KMKerry McGawley
Kerry McGawley
Alun WilliamsAlun Williams
Alun Williams
GMGregoire Millet
Gregoire Millet
Emma HiltonEmma Hilton
Emma Hilton
The International Olympic Committee (IOC) recently published a framework on fairness, inclusion, and nondiscrimination on the basis of gender identity and sex variations. Although we appreciate the IOC's recognition of the role of sports science and medicine in policy development, we disagree with the assertion that the IOC framework is consistent with existing scientific and medical evidence and question its recommendations for implementation. Testosterone exposure during male development results in physical differences between male and female bodies; this process underpins male athletic advantage in muscle mass, strength and power, and endurance and aerobic capacity. The IOC's “no presumption of advantage” principle disregards this reality. Studies show that transgender women (male‐born individuals who identify as women) with suppressed testosterone retain muscle mass, strength, and other physical advantages compared to females; male performance advantage cannot be eliminated with testosterone suppression. The IOC's concept of “meaningful competition” is flawed because fairness of category does not hinge on closely matched performances. The female category ensures fair competition for female athletes by excluding male advantages. Case‐by‐case testing for transgender women may lead to stigmatization and cannot be robustly managed in practice. We argue that eligibility criteria for female competition must consider male development rather than relying on current testosterone levels. Female athletes should be recognized as the key stakeholders in the consultation and decision‐making processes. We urge the IOC to reevaluate the recommendations of their Framework to include a comprehensive understanding of the biological advantages of male development to ensure fairness and safety in female sports.

1 March 2015 in International Journal of Performance Analysis in Sport
Verified
Journal Article
Closed access
CKChristopher Kirk
Christopher Kirk
HHHoward Thomas Hurst
Howard Thomas Hurst
SAStephen Atkins
Stephen Atkins
Tri-axial accelerometry has previously been shown to provide a reliable technique for the assessment of MMA specific activities during isolated training movements. However, this method has yet to be used for the analysis of competition demands. Six male MMA trained participants took part in a single simulated MMA bout each comprising of 3 rounds of 5 minutes with 1 minute rest between rounds. Participants wore a tri-axial accelerometer positioned between the T3-T4 vertebrae in a harness. Mean accumulated player load (PLdACC) and mean accumulated player load per minute (PLdACC.min-1) were calculated for each round and for the bout overall. Capillary blood lactate samples were also taken prior to warm up, post warm up, upon completion of each round and 5 minutes post bout whilst video based time motion analysis was completed post hoc. PLdACC was 224.32 ± 26.59 au, whilst PLdACC.min-1 was 14.91 ± 1.78 au. Participants had a mean post bout lactate of 9.25 ± 2.96 mmol.L whilst there was significant differences in lactate levels across all six sampling points. The group was found to have a work rest ratio (W:R) of 1:1.01 whilst a significant difference was found between bout winners and bout losers in terms of the amount of successful takedowns.

12 August 2020 in Journal of Sports Sciences
Verified
Journal Article
Closed access
CKChristopher Kirk
Christopher Kirk
DCDavid R Clark
David R Clark
CLCarl Langan-Evans
Carl Langan-Evans
JMJames Morton
James Morton
The physical demands of mixed martial arts (MMA) training and competition is not yet well quantified. The Applied Research Model for the Sport Sciences (ARMSS) provides a framework through which to conduct sport science, determining pertinent questions to test research findings in real-world settings. The aim of this review was to evaluate MMA research within the context of ARMSS to critically analyse our understanding of the physical requirements of MMA training and competition. Research databases were searched, with 70 peer-reviewed articles being discussed in relation to the specific stage of the ARMSS in which their results best fit. MMA research was found to be mostly foundational and descriptive in nature and has generally not developed along systematic lines. The internal and external loads and responses to training and competition have not been adequately identified. Therefore, it is not currently possible to state which variables are key predictors of success, or how coaches can optimally manipulate these variables. We propose that MMA research be refocused to be conducted within ARMSS. Specifically, stage 2 studies describing the physical, physiological and technical demands of MMA training and competition, and stage 3 studies determining the physiological predictors of performance should be initially prioritised.

5 January 2021 in Nutrition and Health
Verified
Journal Article
Closed access
PDF file
TWTyler White
Tyler White
CKChristopher Kirk
Christopher Kirk
Background: Brazilian jiu-jitsu (BJJ) is a grappling-based combat sport in which competitors engage in pre-competition acute ‘weight’ loss (AWL) and rapid ‘weight’ loss (RWL) to achieve the body mass (BM) required for their desired division. AWL/RWL practices of UK BJJ competitors have not previously been reported. Aim: Our aim in this study was to determine the prevalence, magnitude and stakeholder influences of AWL and RWL amongst BJJ participants in the United Kingdom (UK). A secondary aim was to explore whether there is any influence of time spent in the sport or competition frequency on AWL/RWL practices. Methods: In this study we used the rapid weight loss questionnaire (RWLQ) adapted for BJJ to determine the prevalence and magnitude of AWL/RWL in UK BJJ, the prevalence of methods used and the key stakeholder influences on these practices. As a secondary investigation we aimed to determine whether there was any effect of age starting BJJ on AWL/RWL. Results: Of 115 completed responses, 59% stated they performed AWL/RWL before competition. Mean BM loss for this competition was 1.9 ± 3.8 kg (2.3 ± 4.6%), with 34% of participants starting BM loss 3–7 days prior and 16% starting 0–2 days prior. Methods used tend to be achieving calorie deficit via exercise and diet rather than hypohydration, with little advice from formally qualified personnel. Participants who perform AWL/RWL started training (BF10 = 199, d = .72) and competing (BF10 = 107, d = .68) in BJJ younger than those who do not perform AWL/RWL. Conclusions: AWL/RWL is prevalent in UK BJJ, but not at the magnitude of other combat sports or countries. Though negative effects of extreme hypohydration are unlikely, there may be a higher chance of eating disorders in BJJ, particularly due to the young age of AWL/RWL commencement.