The hosts will seek a record sixth gold medal at the 25th International Handball Federation (IHF) World Championships, having followed up their victory in Qatar in 2015 with Olympic silver at last summer's Rio Games.

The French men, who have been at the top of their sport for the last decade, are naturally among the favourites, although they will face strong opposition from Denmark, who beat them 28-26 in the Rio final, and Germany, the European champions and Rio bronze medallists.

Others to watch out for include Spain, European finalists in 2016 and eager to make up for missing out on Rio, and Qatar, runners-up to France as hosts of the 2015 World Championships.

What is giving French followers pause as preparations get underway for a Championship that will attract more than 10 million domestic TV viewers for its closing stages, is one of the five rule changes introduced before last year's Olympics - the one which makes it easier for teams to replace their keeper with an extra outfield player.

Under the old rules, if teams wanted to substitute their goalkeeper in order to have seven outfield players on the court, the player coming on had to wear a bib identifying himself as the "stand-in" keeper.

The rule change means it is no longer mandatory for the goalkeeper’s substitute to wear a bib, and the keeper can return in exchange for any of his team-mates on the pitch.

Substituting the keeper now involves a greater gamble, however, as none of the seven outfield players are able to carry out the role of goalkeeper, so cannot retreat within their own goal area.

The new rule makes it a lot easier for the player coming in to attack  - he doesn't need to come back to the substitution area near the halfway line afterwards - and helps the goalkeeper come back faster into play when the team loses the ball, since the player closest to the substitution area can come out for him to come in.

Should the team gambling on all-out attack lose the ball, they are nevertheless vulnerable to the opposing keeper scoring by simply hurling the ball downfield into the untenanted net.

France's star turn Nikola Karabatic has expressed his team's concerns succinctly: "I suffer from this rule more than I enjoy it because I'm more often playing on the favourite side, against a supposedly weaker team that tries something to change the balance of the game."

L’Equipe’s handball specialist, Yann Hildwein, describes it as "the biggest change in the rules of handball since 2000, when the fast re-start was brought in".

He told insidethegames: "This new rule is a real shuffling of the cards for the game. That is the French view. Definitely some of the French players don't like it. They are probably one of the least likely teams to take advantage of it. And there has been some speculation over this.

"In handball you can swap players round while play is going on, like in basketball. In the past you had the right to replace your keeper to gain an extra attacker, but the player coming on had to wear a special jersey, and he was the only one who could be swapped back for the keeper.

"He had the right to go back into his side's defensive zone but he couldn't venture too far upfield because if his side lost possession the opposition keeper could simply throw the ball downfield into the empty net.

"Now you can have seven attacking players, and any one of them can swap with the keeper - it can be whoever is nearest to the bench. So the game is a lot more fluid, it is much easier to switch into all-out attack.

"But it changes the nature of the game.

"Usually the weaker team tries to change the balance of the game by playing with an extra attacker all the time. There are more possibilities to score, it is more complicated to defend against. If you lose the ball the opposing keeper can score simply by throwing into the empty net.

"But it can be very effective. When France played Belgium last month in the European Championship qualifier, Belgium decided to play with seven attackers throughout the match and they scored 37 points. France have been the best team in the world over the last 10 years, and they only managed to win by one point. They almost lost.

"It was totally unexpected. Belgium have never been a strong team. But they managed to keep possession during their attacks and so the gamble worked for them. Under the old rules they would probably have lost by 10 points.

"In the Rio 2016 qualifying stages Croatia beat France 29-28. Croatia are a strong team, but they used the new tactic - not as much as Belgium, but they used it a lot. And they were very efficient.

"In the past it has mainly been teams from Germany, Sweden and Denmark who have brought on an extra attacker for their goalkeeper. France have hardly ever taken that option - they do not have this culture."

That said, Hildwein points out that Denmark used the seven-man-attack option for the first 20 minutes of the Olympic final before abandoning it.

"It didn’t work for them," he said. "France scored two or three goals by simply throwing the ball back downfield into the empty net. So Denmark switched back to the more conventional tactics, and they won the gold."

Overall, however, Hildwein feels concerned about this seismic shift.

"In my opinion this latest rule change has been too fast," he said. "The IHF shouldn't have brought it in before the Rio 2016 Games. It changes the nature of the game - there is much more unbalanced play with the extra player on, there are a lot more empty net shots.

"Also if a player is excluded then teams can help cover by bringing the extra attacker on which means the sanction is in effect much weaker."

The other new rule changes by the IHF involve players treated on court having to leave the action for their team’s next three attacks; teams deemed guilty of "passive play" having to take a shot after a maximum of six passes; players committing fouls in the final 30 seconds being disqualified and a seven-metre throw going to the opposition; and the introduction of a blue card to be shown to disqualified players who will face further action by the Disciplinary Committee.

Despite the doubt expressed over the goalkeeper-replacement ruling in particular, the IHF remains upbeat.

"It should be stressed that this new rule had a positive feedback and is considered spectacular by spectators, many representatives of other sports federations and International Olympic Committee members," an IHF spokesman told insidethegames.

"Especially, the possibility for goalkeepers to score was well-received.

"All the new rules have shown a great success, after a survey with coaches, referees, technical delegates - even the rule about play without a goalkeeper.

"Of course the teams need more time for training and to apply new tactical possibilities. In the next IHF Symposium, which will take place in Paris from January 10 to 14, all these rules will be discussed.

"The IHF aims to continuously increase the attractiveness of handball. Part of this is the ongoing discussion on the improvement and further development of the rules of the game.

"The new rules were first tested at the 2015 Men’s Junior World Championship and since then applied at five further major handball events.

"The overall experience has been positive up to now, even though the teams certainly still need some more time to make full use of the potential of each rule."

This latest group of rule changes was put into motion at the second IHF Forum for the Future of Handball in 2014, when IHF experts and international top coaches from leading handball nations - including Staffan Olsson, Talant Dujshebaev, Gudmundur Gudmundsson, Ulrik Wilbek, Michael Biegler and Heiner Brand - discussed how the attractiveness of handball could be increased and how "negative developments" during the matches could be minimised.

"The two rules concerning an injured player and passive play have been the ones most widely accepted," the IHF spokesman said. "The former resulting in less interruptions and a better game flow, the latter providing referees with a more objective criterion for their decision-making.

"The purpose of the rule on the last 30 seconds of the game clearly is to prevent irregular, excessively unfair behaviour during the crucial period at the end of the game.

"Especially in the last seconds of a close match, a team might try to prevent an attack or a throw on goal through a foul or unsportsmanlike behaviour. In the past, that team put up with a possible disqualification of the guilty player, followed by disciplinary actions, as the player's actions could be decisive for the success of the team.

"The teams still need to grow accustomed to this rule in particular, although it is relatively similar to the old rule on the last minute of the game, the difference being that now the referees must give a seven-metres throw instead of issuing a written report.

"The rule on substituting the goalkeeper for an additional court player can be considered the most controversial one, though the debate had been even more heated.

"New tactical opportunities have emerged from the use of this rule during two-minute suspensions, allowing teams to keep to their handball play even in numerical inferiority.

"An actual seven-against-six play was hardly used by the teams participating in the Olympic handball tournaments, although Denmark applied this strategy during the first 20 minutes of the men’s Olympic final. It will be interesting to see whether and how this rule will have an influence in the tournaments to come.

"Up to now, the teams are still struggling to understand whether a clear goal-scoring opportunity is about to emerge from a seven-against-six situation or not, owing to the fact that the goalkeeper has been substituted and the goal is empty.

"In the same way, the referees need to develop an increased awareness of these situations since their decision-making may differ, depending on whether the goalkeeper is given the opportunity to save a long shot on goal or not."

The goalkeeper-substitution rule aside, Hildwein broadly concurs with this analysis. 

"The other rules changes are fine, they are common sense," he said. "The blue card, people don't care too much about it. It's very good to sanction during the last 30 seconds. There used to be very bad fouls in the middle of the field near the end of matches from sides that were maybe one goal ahead and wanted to protect the win. I think this rule is a lot better, and I think most people agree with it.

"The six-passes rule for passive play is good as well. This rule makes it more objective - you can have no more than six passes. This has stopped a lot of passive play and time wasting."

The video technology system the IHF is employing at the World Championships is hugely innovative.

As well as being consulted directly over decisions, referees will have access to footage relating to incidents that have taken place outside their field of vision.

The IHF introduced a video proof system at the 2015 Men's World Championships, but at the Women’s World Championships held later that year in Denmark it was abandoned after three days when an IHF official failed to allow what should have been a goal for South Korea. He was shown the wrong piece of goal-line video footage relating to the ball bouncing down over the line off the bar.

The refined system being employed at the forthcoming Championships - in which the hosts will get the defence of their title underway in the opening match against Brazil on Wednesday (January 11) - will have a wider remit than the original one.

"The most important change is the direct participation of the referees in the final decision, until now only the IHF official had the right to take a decision," an IHF official told insidethegames.

"We have reinforced one situation: when a serious and unfair action happens outside the field of view of the referees.

"The IHF wants to avoid any negative image of our sport."

The IHF official added that the extent of the video proof system had been enlarged since 2015.

"We'll use the video proof in some new cases," he said. "When referees are not sure if a player deserves a red or a blue card.

"Situations when referees have strong doubts in relation with the last 30 seconds rule involving the red card and seven-metres throws.

"Situations in the last 30 seconds of the match when the defending team has no goalkeeper; if the referees are not sure if the decision must be a seven-metres throw or not.

"The last two cases only when the situation is crucial for the final score of the match."

The technology will also embrace the areas involved in the last men’s World Championships - it will be used for goal-line technology, and to check if the ball crossed the goal line before or after the final buzzer of each half of the game.

The IHF spokesman added: "In Denmark what happened was a mixture of human and technology mistakes. Now IHF has selected a new company from several applicants, Broadcast Solutions, from Germany, the same company which is now working with FIFA.

"The protocol to follow in each case is now very strict, the referees and officials must follow it. In most of the cases only the referees will be the responsible of the final decision, the official can help only if necessary.

"So the quality and the security is guaranteed. With the direct participation of the referees in the procedure, together with the officials, we can be assured of the correct final decisions."