To reduce athlete testing time, the aim of this study was to investigate the relationship between the Yo-Yo intermittent recovery test levels 1 (IR1) and 2 (IR2) performances, maximal sprinting speed (10, 20, and 35 m), repeated sprint ability (RSA; 7 × 35 m), and submaximal heart rates (HRs) after 2 and 4 minutes of the Yo-Yo IR tests by testing 57 high-level soccer players. All players played regularly in one of 3 highest levels of Norwegian soccer and were tested during 3 sessions on 3 consecutive days. Large correlations were observed between Yo-Yo IR1 and IR2 test performances (r = 0.753, p ≤ 0.05). Small and moderate correlations were found between 20- and 35-m sprinting speed and Yo-Yo IR1 performance (r = -0.289 and -0.321, respectively, p ≤ 0.05), whereas 35-m sprinting speed correlated moderately to Yo-Yo IR2 performance (r = -0.371, p ≤ 0.05). Repeated sprint ability at 10, 20, and 35 m all showed moderate to large correlations to Yo-Yo IR1 performance (r = -0.337 to -0.573, p ≤ 0.05). Repeated sprint ability at 20 m (r = -0.348, p ≤ 0.05) and 35 m (r = -0.552, p ≤ 0.01) correlated moderately and largely to Yo-Yo IR2 performance. In addition, moderate and large correlations were found between submaximal Yo-Yo IR1 HRs after 2 (r = -0.483, p ≤ 0.01) and 4 minutes (r = -0.655, p ≤ 0.01) and Yo-Yo IR1 performance, and 2 minutes Yo-Yo IR2 HR and Yo-Yo IR2 performance (r = -0.530, p ≤ 0.01). Intraclass correlation measures of submaximal HR after 2 and 4 minutes of Yo-Yo IR1 test and after 2 minutes of the Yo-Yo IR2 were 0.92 (coefficient of variation [CV] = 4.1%, n = 33), 0.93 (CV = 3.8%, n = 33), and 0.72 (CV = 2.9%, n = 10). Adjusted ordinary least square (OLS) regressions revealed associations (p ≤ 0.05) between sprint speed at 20 and 35 m and Yo-Yo IR1 test performance, but only between 35 m and IR2 test performance (p ≤ 0.05). Further, OLS showed that RSA at 35 m was related to both levels of the Yo-Yo IR test (p ≤ 0.01), and that submaximal HRs after 2 and 4 minutes were independently associated with Yo-Yo IR1 and IR2 performances (p ≤ 0.01). In conclusion, Yo-Yo IR1 and 2 test performances, as well as sprint and RSA performances, correlated very largely, and it may therefore be considered using only one of the Yo-Yo tests and a RSA test, in a general soccer-specific field test protocol. The submaximal HR measures during Yo-Yo tests are reproducible and may be used for frequent, time-efficient, and nonexhaustive testing of intermittent exercise capacity of high-level soccer players.

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Rising demand for water in water-scarce areas has led to frequent predictions of looming ''water wars,'' although evidence suggests that water is also an important source of cooperation. This paper follows up on recent research suggesting that river disagreements are more likely to lead to both militarized conflict and peaceful negotiations when water demands and water scarcity are greatest, but that river treaties have generally prevented militarization while increasing negotiations. Here, we examine the effectiveness of these negotiations, in order to determine whether factors that promote negotiation onset have different effects on negotiation outcomes. Empirical analysis suggests that negotiations are most likely to succeed when they concern rivers with high value for the negotiating states (with many uses offering the possibility of negotiating tradeoffs), when they concern a current rather than future problem, and when the adversaries share closer overall relations, but less likely when water scarcity is more acute and when they involve a crossborder river with a stronger upstream state.