The force-vector theory contends that horizontal exercises are more specific to horizontal sports skills. In this context, the focus is on horizontal force production relative to the global coordinate frame. However, according to the principle of dynamic correspondence, the direction of force relative to the athlete is more important, and thus the basis for the force-vector theory is flawed. The purpose of this study was therefore to test the force-vector theory. According to the force-vector theory, hip thrust is a horizontally loaded exercise, and so hip thrust training would be expected to create greater improvements in horizontal jump performance than vertical jump performance. Eleven collegiate female athletes aged 18–24 years completed a 14-week hip thrust training programme. Pre and post testing was used to measure the following: vertical squat jump, vertical countermovement jump, horizontal squat jump, horizontal countermovement jump and hip thrust 3 repetition maximum (3RM). Subjects improved their 3 repetition maximum hip thrust performance by 33.0% (d = 1.399, p < 0.001, η² = 0.784) and their vertical and horizontal jump performance (improvements ranged from 5.4–7.7%; d = 0.371–0.477, p = 0.004, η² = 0.585). However, there were no differences in the magnitude of the improvement between horizontal and vertical jumping (p = 0.561, η² = 0.035). The results of this study are contrary to the predictions of the force-vector theory. Furthermore, this paper concludes with an analysis of the force-vector theory, presenting the mechanical inconsistencies in the theory. Coaches should use the well established principle of dynamic correspondence in order to assess the mechanical similarity of exercises to sports skills.

Burrows, AP, Cleather, D, Mahaffey, R, and Cimadoro, G. Kinetic and electromyographic responses to traditional and assisted Nordic hamstring exercise. J Strength Cond Res 34(10): 2715–2724, 2020—The Nordic hamstring exercise (NHE) is performed to increase hamstring strength, elicit morphological changes, and reduce injury risk. However, to date, the NHE assisted by the means of an external resistance has not been investigated. Thus, this study compared the eccentric knee flexor strength, rating of perceived exertion (RPE), and electromyographic responses of the biceps femoris (BF) and semitendinosus (ST) when performing the NHE under assisted or unassisted conditions. Sixteen professional soccer players (aged 19.4 ± 2.2 years) performed 5 sets of 3 NHE unassisted and with assisting loads (5–20% of the body mass) using the Keiser machine. Eccentric knee flexor strength was measured from the subjects' dominant limb. Peak surface electromyography (sEMG) of the BF and ST was recorded from the dominant limb; the ratio was also calculated. Subjects rated the intensity of each condition of the NHE on a ten-point RPE Borg scale. All assisted conditions displayed significantly lower (p < 0.05) absolute and relative eccentric knee flexor strength than unassisted conditions. Rating of perceived exertion for each loading condition was significantly lower (p < 0.05) as the assisting load increased except for the difference between the 10 and 15% assisted conditions. Surface electromyography of the BF and ST was not significantly lower (p < 0.05) during all assisted conditions compared with the unassisted NHE, neither there were significant between-muscle differences or sEMG ratios. Our findings suggest that the assisted NHE reduces the load and difficulty of the exercise. Practitioners can use the assisted NHE to manipulate intensity and difficulty if that is appropriate for their programming.

Muay Thai fighters strongly rely on the use of the roundhouse kick due to its effectiveness (i.e. power) and implications on the final score. Therefore, different striking tempos at full power are used during training as a method to enhance kicking power. However, the neuromuscular responses are unknown. Thus, the goal of this study was to investigate neuromuscular responses to a single bout of shorter (every second = H1) and longer (every 3 s = H3) kick striking time intervals, measured with the countermovement jump (CMJ). Nine professional Muay Thai fighters participated in this randomized, cross-over trial. CMJs were measured on force plates before and after (at 0, 5, 10, 20, and 30 minutes) two striking (1 set ×20 reps) conditions (H1; H3). Although no difference was observed between H1 and H3 values, neuromuscular fatigue parameters displayed different patterns over time. CMJ height decreased immediately after H3 striking (P<0.05), whereas for H1 condition CMJ height decreased from 20 minutes as compared to baseline (P<0.05). Peak force in H3 condition was significantly lower at 10, 20, and 30 minutes as compared to baseline. For H1, peak force values were lower than baseline only at 30 minutes. Peak power was significantly lower than baseline for both middle kick procedures. A slight but significant increase was observed at 5 minutes for H3 condition but decreased further at 10 minutes and remained constant during subsequent tests. In contrast, for H1 condition, peak power remained unaffected after 10 minutes, whereas it decreased at 20 and 30 minutes only when compared to minute 0. Results showed that both kick striking modes provoke comparable neuromuscular fatigue but H3 condition showed the potential to induce post activation potentiation. Muay Thai and conditioning coaches should focus on hard striking with both long and slow pacing during specific heavy bag or pad work.

Nowadays, fixed gear competitions on outdoor circuits such as criteriums are regularly organized worldwide. To date, no study has investigated this alternative form of cycling. The purpose of the present study was to examine fixed gear performance indexes and to characterize physiological determinants of fixed gear cyclists. This study was carried out in two parts. Part 1 (n = 36) examined correlations between performance indexes obtained during a real fixed gear criterium (time trial, fastest laps, averaged lap time during races, fatigue indexes) and during a sprint track time trial. Part 2 (n = 9) examined correlations between the recorded performance indexes and some aerobic and anaerobic performance outputs (VO_2max, maximal aerobic power, knee extensor and knee flexor maximal voluntary torque, vertical jump height and performance during a modified Wingate test). Results from Part 1 indicated significant correlations between fixed gear final performance (i.e. average lap time during the finals) and single lap time (time trial, fastest lap during races and sprint track time trial). In addition, results from Part 2 revealed significant correlations between fixed gear performance and aerobic indicators (VO_2max and maximal aerobic power). However, no significant relationship was obtained between fixed gear cycling and anaerobic qualities such as strength. Similarly to traditional cycling disciplines, we concluded that fixed gear cycling is mainly limited by aerobic capacity, particularly criteriums final performance. However, specific skills including technical competency should be considered.

BACKGROUND: Japanese kickboxing is a combat sport designed to accommodate fighters from different combat sports styles. However, the physiological profile of this discipline is unknown. Therefore, this study describes the neuromuscular, metabolic and cognitive responses to an official Japanese kickboxing (K-1) fight in 8 kickboxers. METHODS: Measurements before and after the competition involved a simple reaction time test (SRT), countermovement jump (CMJ), blood lactate (BLA) and rating of perceived exertion (RPE). Additionally, each participant's volume of strikes was extracted from a match-analysis. RESULTS: CMJ height was unaffected by the fight (P=0.230 max, P=0.208 mean). SRT increased postfight (P=0.004). Peak BLA concentration was 15.3 +/- 1.6 mmoL.L-1 at 2 minutes postfight. RPE increased postfight (P<0.001). Match-analysis showed 86 +/- 23 total blows. For rounds 1, 2 and 3, blow distribution was 32.7%, 32.6% and 34.7%, respectively. Total punches were significantly greater (P<0.001) than lame-strikes. Total kicks were also significantly greater than knee-strikes (P=0.002). No difference was found between numbers of punches and kicks (P=0.952). There was a positive correlation (P=.029; r=0.76) between the sum of all strikes in the first two rounds and Delta BLA. CONCLUSIONS: The data obtained here indicate that K-1 fighters need to improve tolerance to lactate accumulation to perform greater number of actions. Furthermore, the results of this study suggest that CMJ height was not sensitive to specific acute fatigue induced by fighting.